I'm sorry. You will find on this site, this is not a unique problem you are having.

Try really really having a heart to heart conversation with your fiance. If that doesn't work, try counselling. I recommend trying one or both soon to get to the bottom of things - don't waste more of your life than you have to!

If neither of those things work, you will have to decide if you can stay in a relationship in which you are marginalized (and maybe worse) when his child is around. Also think about your possible future children. They also will likely be treated differently.

is right on the money.  This is something you have to workout and in fast time. You already spent 4 years on this.  You are not going to change BM. But your SO has to have your back. If he wants to be a couple with SS,  then you know where you place in this team is.  Left out

Maybe you're on their team but you're the benchwarmer.  You know, the one who only gets to play when it's convenient for the team and you won't really be noticed.  Fiance calls you to sub when skid and BM aren't around. BM majorly fouls you by hitting you in the face but the ref (fiance) looks the other way because she's an important team player and you're not.  

I would ask why you stay but I'm sure the answer is that you loooove him and the two of you are so perfect as long as BM and skid aren't in the picture. Also you've put in 4 years and if you can just prove yourself to them this will all work out, you'll get married and play happy family.  I really want to help you see this situation from the outside in. You're being used and abused, you'll never be good enough for them no matter what you do. You deserve a better life than this.  

Honey, I hate to tell you but if you want to be the star player you've signed yourself to the wrong team. Your current contract reads: Water boy (girl)/Benchwarmer.  

You lost me at the point where the XW/BM punched you in the face.

I would have shot her for that crap were I you.

That your ball-less wonder non man of a DH tolerates her crap makes him a write off in my opinion.

Boot his ass out.

Move on to your next adventure and never again tolerate an SO that puts you second to anyone or anything.

Take care of you.

You have 2 separate issues here...

1. A husband issue. You and he are a team. That doesn't change regardless of who is around, including children.

2. SM issue. That will never change unless the BM suddenly removes her toxicity from your life, including the PAS'ing of the child.

First you need to step back and understand the SS has 2 parents. Let them handle all the parenting. Everything. Cooking, cleaning, laundry, chauferring, etc. You are dad's wife and that means your roll is to support him. If he and his child and BM want that to look differently, the ball is in their court.

Then you take back your place. You are DH's partner. If he cannot give that to you 100% of the time - well then it isn't a relationship. It is a convenience. And you need to decide if you are willing to continue down that path.

(Fiancee is for an engaged woman, fiance is for an engaged man)

Why are you still there? He allows his ex to physically harm you and treats you like crap when his son is there.  There are lots of men in the world, even men with difficult exes and children, who would not behave this way -  I know, because I have one.  If BM ever punched me in the face, I think DH would be sitting in jail shortly thereafter.

Give it up. Find a man who loves you enough to have your back in difficult situations. This one does not.

Going on several years, this situation is pretty deeply rooted.

First, the decree says what will happen. Not your Fiance, not his trashy ex. PERIOD. Ask your F if you can go over that part of the decree and reassure him that if his ex OR him was to deprive the other of custody, it'd mean JAIL TIME. If my ex would have pulled that BS on me, I would have had great pleasure in calling someone, to find out what the options were. "Madam, I know this pickup time is difficult for you, however, we agreed to these terms in court, and we are bound BY LAW to abide by them. If you'd rather give me 100% custody, let me know, and I'll get that ball rolling - until then, please just follow the decree that you agreed to follow. There's nothing new or different, so this should be old hat to us all." He should say something like that to HER.

Second, to your F, say, "Listen closely, darling... I will say this once, and only once - I can't believe I'm having to say it at all... I put you first, always. You are the cherished centerpiece of my life. I love you in all ways. I would give you a kidney if you needed one. As long as we are together, I am - and will be - the eyes in the back of your head, the ears in the other room, your wingman in life, your tail gunner in battle, your calcuim in your spine, and the fulcrum to your lever in all things that seem impossible. You see this and surely can agree, right?"

(get him to agree, or you'll need to discuss it before proceeding)

Continue: "I need you to be all those things for me. I need you to show your kid how awesome I am. I need you to purge the negativity his demonicmom fills him with, and refill him with that awesomeness that YOU have. Make him a reflection of YOU, not HER. When you have him over, tell him... TELL him... PLEASE TELL HIM... that I haven't replaced him in your life, but I am here to complement you, to bring you joy, and tell him how I AM all that to you, and I DO all that for you. Tell him that anyone who says anything different is straight up mistaken because they don't live here and can't possibly know."

Have him explain this to that boy. The kid needs to hear it.

I had to have a similar chat with DW, we're coming up on 4 years as well. Look at my posts a couple weeks back to see what I did, and it worked great, though my situation is a little different and I had to deal with a couple of teens. I sat them down and let them choose the relationship they'd have with me, and it was GREAT. We broke new ground.

Best of luck!