My (f40) boyfriend (m56) of 4 yrs does nothing about his child’s behavior and it ruined/is ruining our relationship.

So my bf’s 14 yr old daughter is a menace.
Most recently while my father was dropping them off at the airport for their annual trip that (I opted out of b/c last years was 2 weeks of horror instead of vacation.) She decided to take the gun she was chewing out of her mouth and stick it under the seat of my fathers brand new truck. I waited til he got home to tell him so that the vacation went ruined. When I told him he went in her room and found dirty used tampons hidden everywhere (a ongoing problem), her room and bathroom a complete and utter mess (as per usual), and an X rated book hidden in the sleeve of another book. He told me he was taking her phone away amongst other things.
She was to clean her room and keep it clean and to throw the tampons away properly.
A couple days later they are back and I find out that he is having someone come to our home to fix her phone. $200 later (cracked screen) they find that the phone is hacked anyway.
After that I immediately shut down because everything he said he was going to do he went back on. While telling him about my Dads truck I also told him how her and her sister were left alone so the mother could go to Minnesota. (She told him she was taking them). While she was away the 14 yr old stole $60 from her, snuck out the back door (to avoid Ring), and met her friends for sushi, all while the 17 yr old sister who was in charge had no clue. Once the mother found out the 17 yr old got in more trouble for dirty clothes on the floor than the 14 yr old thief.
Now I am being accused of not liking his children, and we are breaking up. His excuse is the way I talk to him, (when you are being called a loser it’s hard to stay calm) mine is how he went back on everything he said, didn’t call my father to apologize and the fact that once again the 14 yr had no repercussions. The tampons have been an ongoing problem. She hides them in her dresser drawers, in her bathroom drawers.
Today we both went in her room and a tampon applicator was sitting on her floor 5 inches from her trash can. Room was a DISASTER. And she hasn’t even been here!!!
(I found out they had Covid and not from him!!!)
Someone please help me understand whether I am in the wrong?
He did try to talk to the ex wife but she was “too busy” and called him a drunk. Their co parenting is the worst I have EVER seen in my entire life of knowing any and all parents who co parent. She is entitled, spoiled rotten, a manipulator, deceptive, a pig, lazy, and now a thief! Her mother broke into her fathers home in HS and stole a bunch of things.
The 14yr old looks like him but talks and acts just like the mother. I’m afraid if he doesn’t do something she will get worse.
He claims his children are his life, but yet is out with his friends every weekend he has them.
I don’t understand why I’m good enough for pick ups or drop offs when he’s busy but I can’t have a say in her behavior. Him and the ex both reward this behavior. I feel so bad for the 17 yr old. She gets treated like crap by the mom and then when she’s at dad he’s not here and she sees her sister not get in trouble and either homes. It’s just so frustrating.