My mans Ex😲

My fiance was married for twelve years and has two children 9 and 3. He has custody. They divorced because she cheated on him. Both boys look nothing like either one of them..I can't stop trying to find a tiny piece of their dad in them..I can't!! and it drives me crazy. The boys are sweet but every time I do things with the boys she gets jealous and wants to visit them. They have been divorced a year and half and still contacts him all the time. We are getting married soon and we have been trying for a baby. I feel like giving up because it's like he already has a family. I've never married and I have a son that's a senior and I'm starting all over for what I ask myself? Drama? Any advice ?