Can I accept his child

I been with my boyfriend 11 years we split up for about a year and a half and I was dating other guys and as much as my ex then trying to get back together I wasn't ready,he the slept with someone who got pregnant and kept the child against his wishes.After thinking long and hard I decided I wNted to be with him again and now the baby is 6 months old,he has not seen his child as he wasn't ready and this wasn't how it was meant to be,it should have been me and him having a baby.He now wants to start being a father to that child and wants my support but can I do it,he didn't cheat or lie but please understand this is hard for me,I really hope I can support him through this but it's hard accepting that this woman will always be in our lives.What do I do I'm so torn,I live him and we our trying for our own (I had a miscarriage 6weeks ago)such a difficult situation....any advise please ladies.Am I stupid for staying and trying to support him and this innocent child x