Problems with partner’s ex wife

Not sure where to start, this post isn’t so much about my partner’s child, but more about his ex wife whose behaviour is starting to cause a problem in the relationship.

I have been with my partner (40M) for the past 6 years. I knew him before we got together and I knew that he had a good friendly relationship with his ex wife (47F) before getting into the relationship. This didn’t bother me, initially I thought that this was a very positive thing for their daughter - who is now 12 years old. They share 50/50 custody and me and my partner live 5 mins away from his ex wife so that he could be close to his daughter. Again this arrangement didn’t bother me too much in the early stages of our relationship. They separated when their daughter was 1 years old, mostly because he was forced into a life he never wanted and felt stuck (he never wanted marriage or kids). I know they loved each other deeply, but my partner had to move on.

He remained single for a few years when he met me, and I naively thought that things would be ok since the ex wife (who never moved on or met someone else) would not be much of a problem. When she found out about me she started being difficult with my ex and attempted to limit his time with his daughter. This stopped after a while, but when she found out I met his daughter (1.5 years into our relationship) and was spending time with them both, she also started causing issues.

With time these issues settled, but she would still at times message him late at night telling him about how she’s crying because she feels lonely, how devastated she is that their marriage broke down, and how she always wanted to have a family unit but she doesn’t have that anymore. Sometimes she would even open up about failed dates that she’s had. Through all this, my partner would listen to her and tell her that he wants her to move on but keep an appropriate distance. I didn’t mind this because he would tell me everything and we both mostly pitied her. This anxious behaviour with time started rubbing off on the daughter, and that, mixed with my partner’s tendency to parent from guilt has led to the daughter not having the appropriate emotional maturity or independence for her age. One big example of this is that she still needs her dad by her side to go to sleep, always trying to postpone bedtime, and has started to develop manipulation tactics so that she is always the centre of attention, behaviours that are now bothering me especially since she’s 12 and should be starting to mature slowly.

The most recent experience that ticked me off about his ex wife’s behaviour is that she sent their daughter to my partner’s place with a small stack of old birthday/thank you cards that belonged to my partner that were still in their marital home. He didn’t look at them, but when I got home and found them on our kitchen table I innocently looked through them, and amongst the stack I found two love notes that she had written to him when they were still married (I know this because she had written the dates on them). I was shocked, and my partner, to his credit, who was also shocked and perhaps ashamed of her behaviour, threw them away instantly. We didn’t discuss this further, although I wish we did because I have been internally raging about this since.

My question is - is this normal? How do I approach the situation so that my partner can establish firm boundaries?

I think its also important to mention that because I know how sensitive my partner’s ex wife is, I don’t really share pictures with my partner on social media, but on the rare occasion that they both hang out together with their daughter, she is always happily sharing pictures of them as a family. This has led to a lot of resentment that I don’t feel I can share with my partner or anyone else. Any advice?