Sleeping with a friend of x (advice needed)

Oakyyyyy. No judge zone!

My x boyfriend and I had a mutual friend. (More so his friend) and he would hang around us but always told me to me I deserved better. (My x was cheater, liar and abusive) he would be the one to pick him up when he acted psycho and tried fight me.

It’s been 2 and half years since I dated or spoken to my x. Him and my x barley hang or speak anymore but are cordial.

How bad is it that I am taking to this guy now and sleeping with him? He’s amazing 😫 should I feel bad towards my x? I don’t owe him anything. . Or is this crossing boundaries. Please help I feel like worse fucking person. Even though my x did far worse. I can’t take it back now.