I feel like he's cheating

I am 33 weeks pregnant with our second baby and for the past two months my S/O has refused to be physical with me much less emotional we barley hug, kiss, or even sit together! He works full time and does night school from home for a couple hours a night..when he's not doing school work he's on his phone or his game he got home from work and stayed on the phone outside for like 3 hours he said it was his brother..okay that I believe but two hours later he was on the phone in our room and when he came out I asked who called twice and he ignored me he's been going places on the weekend more than usual and it's always for 3-5 hours he tells me he is either helping his friend or his brother/'s ...I don't think he is cheating on me or its more I don't want to believe he is..it just doesn't make sense why for the past two months he's been so distant from me..I've tried to be sexy for him but he just turns me down saying he's tired..i just feel like if he isn't getting it from me where is he getting it from..is this just my hormones or should I be worried..