I certainly wouldn't want BM in my house. 

There was no reason to invite BM over, especailly without clearing it with you guys, first. Your home should be BM free at all times. That's my motto.

Maybe she thought losing the cat was life or death

idk I wouldn't want some beastly breeder up in my personal space either. 
 

maybe install some cams just in case she tries it again you can see what she's doing even tell her to get out or tell your so to tell her not to set her pinky toe beyond the driveway curb

Nobody wants their SO's ex in their house without their permission. Nobody. Obv Princess can't handle catsitting so don't have her do it anymore. She should stay with her mommy when you guys are gone since she needs her so much.

This enmeshed codependent family isn't going to change. 

I'm not making excuses and I positively never wanted BM here in the house.  But, this girl is only 17.  My guess is she freaked out about the cat and, without thinking it through, called her mom for help.  Your SD doesn't sound like she's quite up to pet sitting yet.

This was his idear fo cr pet sitting and SD with the result of BM coming over   It's time for DH to redecorate your home.  Paint all the rooms, replacing all the floors.   Replace the furniture.   A new home with out BM.  Personally I don't know wast I would do. What a underhand thing  

over  

"DuH, why would I be OK with the woman you used to fuck raking around in my home and snooping through my belongings?"

Did they at least find the cat?

Rocky, it would not have been necessary for me to fuss over a BM invasion because my husband would have blown his top before I had a chance to complain. Ugh! The very thought of my husband’s ex-wife rummaging through my things, snooping around my house for dust and grime, makes my gorge rise. 

She was there, searching, for an hour?! I’ll bet the farm that there wasn’t a single nook or cranny that escaped her scrutiny. Hon, I’d be livid! At the risk of giving offence, I’m convinced that your partner is more enmeshed with his former family than he will ever be with you.

 The fact that you’re afraid to speak your mind is very telling. Hon, I’d be screaming so loud and furiously that the neighbours would hear every word. Leave the dumbass, for Pete’s sake! He’ll never change.

Ugh it's sickening when this happens!! No you are not overreacting !

It happened to me in 2020. At that point BM had not been in our house for two and half years..

She used our dying dog (which was never hers only SOs) as an excuse to come in. While we were both at work and she was randomly picking up SD... She put SD (then 13) in an awkward position... she asked her to come into the house...

I saw this on the cameras a day later. None of the kids had mentioned it to us that BM came in...

She was in the house for 8 minutes... My head was spinning when I saw it on the cameras. When SO called me on break I demanded he do something about this and let her know she wasn't welcome.

He did.. she started crying and then her husband called SO... and agreed with him. 

SO DID blame me for it though..in a round about way... which I him corrected later about... 

all you can do is make sure there isn't a next time. "I've worked it out w/ friend/neighbor/animal motel to take care of kitty while we're gone. After what happened last time it just isn't fair for poor SD to struggle through it again."

You asked why you are still in this relationship, and you said you don't want to leave because you don't want to be alone. You have answered your own question. What you have to understand is being alone after the end of a relationship is only temporary. If you want a new relationship, you will find one - after you have "done the work" and healed from this one first! Fear of being alone is not a good reason to stay in a relationship that is making you miserable on a daily basis . Your DH is never going to put you first and he is never going to take your feelings into consideration and that does not work for you.

We have had several members of this site leave their partners and every single one of them has ended up happier. Most ended up in new relationships that are healthier and happier or discovered they were perfectly content to be on their own. You can do it too! You have tried every way you can to make this work, and because it is only you trying, things are never going to change. You are not too sensitive - you need to get mad at this situation so you can take action to make it better.

No, you are not being overly sensitive. I would absolutely go crazy if BM was ever to set foot in my house. I think almost all of us here would! 

I don't want to be harsh, but you say you won't leave because you're afraid of being alone. But in many, many ways you already ARE alone. Sure you have the physical presence of another human. But this man is not "with" you because he is never on your side. He's disregarded your wishes, expectations, requests, and boundaries over and over. You, by yourself, would be better company FOR yourself if you weren't constantly doing the mental and emotional gymnastics it takes to deal with your SO and his kids. And after some time to heal, I can assure you that you could find a better partner, if that's what you want. 

With this, SD has voided all trust IMHO.  She does not invite the toxic opposition parent into the home of a new family under any circumstance without prior approval from both of the spouses in that marriage.

For any reason. 

Time for the full meal deal security system that monitors every square inch of the property and notifies of ever entrance and exit from the property. Had that been in place, you would have been notified, and you could have called the Police when BM set foot on your property. And I would have if I were you.

This is why a long distance visitation schedule is so much less drama filled than  local EOW/EOWE visitation. Neither parent can overstep so easily and kids cannot make related bad decisions as readily.  LD visitation is one of the key contributors to DW, SS, and me being so close and giving us the ability to counter toxicity in the shallow and polluted end of the kid's gene pool.

Accountability for behviors has to be maintained whether the toxic end of things likes it or not, or the toxic parental Kool-Aid drinking failed family progeny like it or not.

Youre not over sensitive and not overreacting. No one wants their ex in their house. I would be horrified... It's an invasion of privacy. My ex and I do not step foot in each other's houses.

Before my husband and I got together bio mom kept trying to get inside his house. One day he was going on a trip and he actually nailed his bedroom shut. She texted him all livid and he told her do not step foot in my house again. And then he rekeyed.

The problem is you know it's a privacy thing and makes you feel violated, rightly so. Your husband is dumb if he doesn't see the issue. 

If your husband was reachable.. then he needed to be asked if mom could help look.

I guess I could see her asking mom if the cat had been joint pet with mom at one time? but stilll.. dad should have been given the option of having his EX help look.

I'm guessing the girl was trying to avoid telling dad she thought the cat was lost on her watch..

To avoid this in the future, follow the advice for it not happening in the future. Hire a cat sitter to come in once a day to check on the critters, feed them, play with them, and love on them.

My SS is a cat guy and when he travels, that is what he does. He was worried about his very high maintenance demanding feline Empress having issues with his absence, separation anxiety, etc...  His cat sitter lady was great. He has Cat Cams all over his apartment.  He checks througout the day and .... no drama. The cat plays readily with the cat sitter, the cat is fine on his return, and .... if he had a kid with a toxic X, there would be zero risk of the X rifling around his home over some bullshit cat emergency.

Cut family out of it.  They far too often disappoint beyond measure over things that do not have to be dramatic.  For damned sure minimize any opportunty for an X to enter your home.

I wouldn't be keen on SD in the house alone. BM in the house is cringey and maybe disrespectful at best, and an invasion of privacy at worst.