thinking im having an affair w step dad?

ive been w my SO for 4, almost 5yrs. when we both freshly married, he tends to accuse me of cheating on him. we were still living w his mom and step dad at that time. there was a time we both were arguing and he was up all on me. he pushed me, i fell and landed between his step dads legs. he started acting like, so i was cheating on him. his step dad was mad and told him to stop being like that to me and if he hits me, hes gonna call the cops. we both moved out after that. we began having our 1st child in our 3rd yr of marriage. just 2wks ago, we went to visit his mom and step dad. his mom was bragging about how were going to have beautiful and handsome kids because her son is so handsome and they got the "good looking" gene from her. his steo dad started saying that its not just because of him, im beautiful too. then yesterday, his step dad called me 7x in the evening, wanting to know about our expected baby due this mth. my SO got very upset, started asking me question like why wont he call him instead. he starts acting like im doing something unappropriate w his step dad. like WTF!? idk what to do anymore! this is so insane!