My fiance doesn't want sex anymore

I'm currently 27 weeks pregnant and for the last maybe two months my fiance is just not feeling having sex with me .. at first it was he's too tired from work and than it was he's stressed out about money and sex hasn't been on his mind .. and than he finally said it's just weird to him to have sex now because I'm pregnant and it's weird. its been making me feel so unwanted and like he isn't attracted to me anymore.. yesterday I accidently walked in on him masterbating and I was so hurt not because he was masterbating or watching porn I usually don't really care but I felt some type of way because we haven't been having sex and when he went to go do it he was sitting in the bedroom with me could of iniated something and when he saw I was bothered by it he just said that hes stressed out and he's sorry he is being distant .. but in my head I think we'll you aren't stressed enough to watch porn but you can't spend some intimate time with me .. I just don't know how to go about the situation when I've talked to him or how to feel like it isn't him not being attracted to me .. or am I just completely overreacting?