Is he cheating?

So my BF and I have been together for almost 5 yrs and we have a 3 yr old and twins on the way. When we first started dating I found a eyelash curler in his room. Obvious thing I assumed he was cheating we fought about it he lied to me saying it was his sisters since he lived with her but soon said it was his and he was embarrassed about it. Whatever I’ve kind of let that go and we continued to date we had our son he moved in and everything has been good. He works 7pm-7am leaves to work at 5:30 because of traffic and gets there at 6:30 and calls me everyday when he gets there. He comes straight home and arrives between 7:15-7:30. He’s a great father and partner and I’ve haven’t had a reason to assume he’s cheating but today took his shirt off in front of me as he was going to shower and I noticed scratches on his back as if it was a claw mark. I asked him who he’s been seeing and of course he got offended by my comment and he said no one that he scratched himself and reached back to prove he could reach that spot but it doesn’t look like a scratch mark it looks more like a claw mark like if someone would have scratched him while having sex. I don’t know what to believe. We haven’t had sex because I’m 30weeks pregnant and haven’t had sex for a while now. Is he cheating on me??