What’s a mother to do

ending her ideas each day but she told me he dads fiancé already purchased her dress and they’ll be planning together 😣 I’m extremely hurt and honestly don’t even want to participate at this point. I spent many years in an abusive relationship with her father. I finally got the balls to leave him about 10 years ago. Three years ago he decided to move away and the kids moved with him. It’s to the point he is turning all our kids against me. We have 3 children together 15,17, 12. I never see my 17 year old because he has a girlfriend and work and now my 15 year old barley comes on the weekends. My 12 year old is the only one that comes each weekend and they make her feel like crap because she does 😢 They constantly make comments like why do you even want to live here go live with your mom since you always want to go there. He dad even told her after he bought all the other kids sneakers he wasn’t buying her any because she was with me over the weekend. He leaves me out of all events and tells me things an hour before hand and believe me this won’t stop me I’ll still show up for my children. This party on the other hand I just don’t want to be there! I know it’s selfish but I’d rather just do something on my own for her. Please give me advice and input thank you