Why do I feel guilty?

My ex broke up with me 3 months ago. Since then I’ve been getting closer to my best guy friend.

We had a falling out due to religious differences, mainly focused on HES waiting till marriage, I didn’t.

Tonight he came over and while hanging out, we kissed, and some other stuff.

My ex and I stayed friends and, for some reason, I feel like I cheated on him.

We havnt talked about getting back together at all, and he’s in fact told me about other girls he’s into. He still will sext me and call me his and such.

Why do I feel guilty? I know my guy friend and I will not go anywhere, it was simply because of hormones.