Blending families

My boyfriend and I have been in a relationship over a year. We have known each other for over 14. He is divorced and has 2 daughters. I am a single mom of an 11 year old. I am also the adult child of alcoholics and have an aversion to family. I don’t have an attachment or typical family functions with mine and never have. He is text book traditional with family. I have always wanted another child, but to be with him I had to sacrifice that desire because he had a vasectomy. Well his daughter is pregnant. Ever since then I have found out that I have nothing but hate and resentment towards him and his family. I want nothing to do with them. It pains me to even look at a picture because it seems to be a slap in the face that his family is doing well and extending the family tree, etc where mine had to come to an abrupt halt. He also pays his pregnant daughters car payment and whatever she needs, even though she is married. She can make no mistakes in his eyes and the fact they have nothing is everyones fault but hers. He expects me to embrace and be excited for his family, holidays and her pregnancy and I can barely keep it together to not lash out. Im afraid this issue is major enough where its destroying our relationship. We were engaged and I broke that off, we have separated family life and are barely roommates who are intimate. Is it fair for him to expect me to just accept his family and embrace them as my own…when he knows how painful and scary a request it is? My biggest fear is when she has the baby he will expect me to miraculously change my mind and jump into a doting grandmother. I dont know if I need to just end the relationship because it is very strained and painful on us both. We are withdrawn and merely civil.