New boyfriend advice?

Hey everyone super long post, but let me give some back story! So I recently just started seeing someone who has a 3 year old. We went to high school together, but never really talked. I bumped into him a few months ago and we kinda just became great friends. We took his daughter to the park and out to eat and get ice cream and it was great. I’d support him when he was trying to hook up with other girls, but then he caught feelings and I can’t deny that I did too. We were taking things slow of course after months of hanging out as just friends and then one night he asked me to be his girlfriend. He’s so amazing! Everything my dream guy would be, but complete opposites. He’s outgoing, funny, talks to everyone and I’m (now) quiet, like to stay in, and keep to myself (Leo vs. Scorpio 😂).

I’ve been in awful abusive relationships and have been cheated on so unfortunately I’m paranoid and insecure. He’s extremely attractive and everywhere we go girls look at him, and I know I should feel lucky, but I just feel insecure. I know his past (which we will get into), but with my depression, anxiety and bipolar, I have so much going through my head at all times. When I bring up my concerns he gets annoyed especially with my depression when I’m really down he tells me to stop and doesn’t understand why I feel that way.

Next, we um I guess technically he’s still married as he’s filing for a divorce from his wife of 6 years who cheated and crushed him, but they’ve been separated for a while now. He’s a great guy I know it, but the way she pushed him and broke him down, I know why it’s his first instinct to get annoyed with my concerns.

Now the most important part! With his daughter I adore her. Love her even. It’s almost like she’s a mini me and equally as sassy, but has anyone else been in this position? How should I deal with this with the soon to be ex wife who’s now saying things to the 3 year old about not liking me and that SHES her mom (like well duh)? I live in a very small town. She knows we are dating, but I have zero tolerance for gossiping. She’s an awful mother who goes out and blows all her money at the bar and then still has the audacity to ask him for money. She will push her daughter off on other people to go out and I don’t hate many people, but I hate her. I’ve wanted to be a mother since I can remember and she’s doing this to the most precious girl I’ve ever met. I just need some advice. How do I not overstep my boundaries with the daughter when she treats me like I’m her second mom? Help! I’m torn, but I’m so happy with them!