Uh-oh, this is not good. Talking and texting, everyday? Telling her that he loves her?

Has he even met the child yet? Does he even know that it is his? This just doesn't sound right.

Wow! So sorry to hear this

Honestly you have a DH problem. He has crossed so many boundaries in your relationship I lost count in this one small post.  

Truth time. Does he want his marriage, and if so then you need to set boundaries and he needs to respect them. Or he wants his old life, and if so then your step problems just came to an abrupt end and you dodged a bullet!

In any case the marriage come first. Above kids. Above exes. Above all else. Or it isn't a marriage  

He said "I love you" to his ex?!?! Um, that would be the end right there for me. There's no way that I would sit back at watch that happen. I feel for you. I hope that you're able to talk to him and maybe go see a councelor about this. He's crossed a line. He's developing a relationship with an ex. Kid or no kid. How would he feel if the tables were turned? I'm sorry. I hope you're able to figure this out. 

Oh no no no. This is a potential marriage-ender. In what world does he think it is ok to tell an ex-gf that he loves her and his new wife should be ok with it? And no, it actually isn't important for him to have a close friendship with her just because she is allegedly the mother of his child that appeared out of nowhere. What is important is for him to have an amicable coparenting relationship with her with boundaries, because he is MARRIED, and even then, most of our DH's get by with less than an amicable coparenting relationship. Either way, there's certainly no need for I love you's in this relationship.

This would be a hard line for me. Either he cuts the crap and maintains his relationship with her at an appropriate level, or he can have her- It sounds like he is already having an emotional affair, right in front of your face.

Boundaries, boundaries, boundaries. You need to be clear about what YOU need, and a loving husband will respect and support that.

As others have asked, have you met the child? I'd also ask for a DNA test.

Your husband is newly "in love" with being a father. Assuming this is actually his child, he should develop a loving relationship with him.This does not need to extend to a loving relationship with the child's mother. Sure, they should be friendly and co-parent but they should not act like a couple because they aren't.

My DH is easy with the "I love yous," including saying that to other women. He doesn't mean it in a romantic way. He means that the person is important and he is a friend. But you can imagine that people take this the wrong way and it has caused a LOT of trouble in our marriage until I insisted that he stop that kind of language. It was a boundary I had to put up. I have guy friends but they don't go around telling me they love me, and if they did, DH would flip. Anyway, that's just a perspective on what the "I love you" might mean between your DH and his ex. But it is inappropriate and he needs to knock it off. That fact that it hurts you should be reason enough.

You are his wife. His ex has zero say on what goes on is your house, and if the child visits his father you are the other adult and authority figure in the house. The child's mother does not get to dictate what role you do or do not play in the child's life. That your husband would actively exclude you is appalling.

What, exactly, does your husband want? If he wants to live the fantasy of his old life, you need to know that so you can move on. He can't have you AND a fantasy world.

Set your nonnegotiable boundaries. Be explicit about what YOU NEED TO BE HAPPY. Have consequences should he cross those boundaries. Example: You will not tell other women that you love them (save for maybe his mother or sister). If you do, then I will think that my feelings don't matter to you. We will attend couples counseling to work through the issue, and if you won't do that I can't stay married to a man who has no concern for my happiness.

I agree with what everyone else has said. 

It sounds like both of you are understandably grieving over the loss of your child together...and your subsequent struggles to conceive. 

Then he finds out he supposedly has a son...and he goes all in right in front of you without involving you in any way? At the very least, that is incredibly, incredibly unkind, selfish...cruel. Of course you feel crushed about this. Your husband should be supporting YOU and your lives together...not off playing "happy family" with some brand new kid of HIS while leaving you to grieve the loss of a yours kid all by yourself. Disgusting. 

If it really is his son...I understand his wanting to have a relationship with him. And he should. But he should go about it in the most sensitive, caring way possible toward you. He should have enough emotional intelligence to understand how hurtful and difficult this will be for you and spare you as much pain as possible. It sounds like, instead, he's doing the exact opposite. 

Your husband is behaving inappropriately.  You've told him it bothers you with no results. So yes, leave. He will see by your actions how much it bothers you, and he will either choose to fix things or he won't. Be the catalyst so you're not living in this unacceptable situation any longer.

I can't even imagine the betrayal you are feeling. Especially under these circumstances... He "loves" the woman who took off pregnant and hid his child from him for 10 years. What, is she divorced now too and is looking for a cash out? Super classy to slip in after you have lost your child. 

Many marriages don't make it after the loss of a child. What you DH is doing is trying to deal with his grief by regressing back to an old relationship and thinking that it is his second chance to be a father (in my humble opinion). He is losing you in this process and can't even see it happening, or is to blind to care. 

Take care of yourself in all of this. Find a good counselor, surround yourself with friends and family. There was a reason that these 2 broke it off years ago and she didn't see fit for their child to be in his life. I seriously doubt they are going to find that missing magic and have some perfect family together. He can't replace the child you lost with one that he didn't care enough about before to even be bothered to find out for sure if he exsisted. 

Ex they have been growing closer and closer and my husband even tells her that he loves her.

^^^^^^^^ this right here is a h@ll NO! They can have conversations about their son but anything other than that and saying I love you is over stepping boundaries to me.

I want to be a step mom but she's made it very clear to me that she doesnt want me having any kind of roll as mom and my husband is on her side about everthing

^^^^^^^^^^^^^^^ Aside from BM your H does not want you to have any part of his sons life so with that being said disengage NOW.

I have tried to explain how strange and upsetting that is for me but he just keeps telling me that it is important for them to have a really great friendship, which I do agree with but to what extent

^^^^^^^^^^^^^^^^You have communicated with your H how you feel and he has dismissed it and has prioritized his so called friendship with his ex over his marriage with you??? He can coparent with her and be civil, nothing else is required.

There are red flags all over the place sweety. Have a heart to heart serious talk with him because this is unexceptable. If he's still not respecting you in any way, shape, or form you should really consider this marriage and what the future will bring if you decide to stay.

this equation. If he's telling this woman who ran off with his kid and he hasn't seen for 10 years that he loves her then he has issues. If you choose to leave, get your ducks in a row first and get a great attorney.

If he is telling his ex I love you (maybe I am misunderstanding, pray tell); you have no marriage. This is highly inappropriate behavior by a husband regardless of circumstances and it appears you realize that now.  Prepare yourself for the end, make certain you document this sort of mess  and be ready to use it when it is needed.  

If you are wise....you will let him go love her....you can do much better than this and you deserve a better life.