Emotionally hurt 😔

So I’m 34 weeks and 4 days pregnant, me and my boyfriend have only been together 1 year but gave known each other for 4 years and have been very close friends before we were dating. At the start of our relationship we weren’t that serious so we both flirted a lot with other friends as we saw it as harmless although inside it did bother us both (we were just too early in the relationship to feel comfortable about bringing it up and we also knew each other well so brushed it off). Anyway, when my boyfriend found out I was pregnant he was really really happy... but he also thinks it might not be his, this is absolutely heart breaking to me because growing up I never had a family I was in and out of foster care and was adopted so I’ve always looked forward to being a family with the person I love someday! To hear from him that he thinks his little boy might not be his and it breaks my heart. I know it’s his little boy but the more he questions me it breaks me. He has been cheated on many times before in a previous relationship and I don’t know if maybe that’s why he doubts me THIS much but I just can’t deal with the fact he wants a DNA test and everything like that it makes my pregnancy experience a little less special and more upsetting. Whenever I reassure him he talks about the start of our relationship when we were flirty and how he thinks maybe I forgot I had sex with someone else and things like that?! He really doesn’t trust me and doesn’t believe me and I just need someone to talk too or some advice. I know a lot of people will be judgey and tell me I haven’t got a good relationship and things like that so please refrain from negativity. Thank you for reading this far❤️