He’s getting tired of me?

So we’ve been doing amazing recently because I’ve changed my ways for him and started doing things for him without him asking, just being kind and generous.

But the other day we had a fight in the morning before he went to work, and when he came home he wanted to have Intercourse so we did. But I’ve been having these gut instincts that he’s been in contact with his ex girlfriend. And that night our sex wasn’t the same, he wouldn’t even close his eyes when he kissed me and this happened several times. But while we were having sex it didn’t feel like it always used to feel, it felt empty. Almost like I was just being used for sex when he wanted it. And in that moment I felt sick to my stomach and almost told him to stop but then he’d know something was wrong and I didn’t wanna ruin his vibe.

I need advice on what to do. Please help. I’m scared he found someone else or is just completely losing interest in me.

Ps. I talked to him about it but he said he was just tired but that wouldn’t explain me feeling like he was distant from me. I know what I feel and it’s been right in the past every time with my past boyfriends.