Pregnant and in doubt

My partner cheated on me 3 years ago with his ex. They have a daughter together. He has one child from a previous relationship and so do I. I thought that I could get over him cheating on me, some days I am really strong and other days I am not and even though I am 36 weeks pregnant with his baby now. I feel to leave the relationship for fear of getting hurt again. He has been really supportive throughout my pregnancy and is happy that we are having a baby together. When I discovered the affair that he had, me and his ex had words. She at first denied that she was sleeping with him and then later on admitted that she had been sleeping with him, started being rude to me, so I started being rude back. The child that they had together is now 18 years old I thought that they both would of moved on in life, like me and my ex we have 16 year old together and try and do things in the interest of our son. Anyway my partner is wanting his daughter to have a relationship with our baby obviously because they will be siblings but am not to keen because of his daughters attitude , she seems very jealous and I think to myself how can an 18 year old be jealous of a newborn. She has been demanding huge amounts of money since knowing of my pregnancy. My partner has been really stressed out. Btw I have never ever met his daughter because of his ex not wanting me too, but he has let me know about comments she has made. I feel to leave this relationship, because its drama I don't need. I dont intend to stop him from seeing our baby, I just cannot trust him anymore.

Sorry to hear you're going through so much at a time when you should be enjoying. I was cheated on before and whilst I remained with that partner I never fully got over it, no matter how nice he was it was always there in the back of my mind. I think sometimes the best thing to do is seek professional help to try to overcome it and if that doesn't help them moving on is the only option. The daughter sounds like she's marking her territory, I understand your frustration. It's a bit wierd you've never met her and yet your expected to let her have a relationship with your baby. So the ex didn't want you meeting the daughter and your partner just allowed that, didn't stand up to her, that's a bit crap. Have you tried talking to your partner and telling him How you feel?