So once again. He thinks I'm cheating on him

Suly

Last night we were having sex when we fished we were just laying down he put a finger in my butt ( I don't let him touch me there I don't like it) he got super serious and ask why was it easy to put it in. And what was I doing. I told him nothing and I didn't know what he was talking about. Then just pushed me aways and turn around.

This the second time he's accused of cheating on him.

I don't get why he would think or believe that.