Leave without explaination

Hi,

I was in a relationship with a guy, but we haven’t defined it. He calls everyday, but I started to step back because of a woman he has in his life that he calls “just a friend”. Many times I told him I feel uncomfortable, they talk everyday. He does nothing about it. They have been intimate, even though she is married. I have to carry that burden of knowing and it stresses me out. He says it was a lapse of judgment and that he was going through grief because his wife died of cancer. He is trying but I can’t see it. I have heard him say to her once he loved her, but he said it meant nothing and saucy text messages. I have been cautious. I have ended it in the past, but he comes back crying saying he want to be with me; but there is something that has been feeling off. I want to just walk away, I don’t want to say anything, just leave. I am so disappointed in myself that I didn’t leave earlier. The lady said she will stay with him no matter what to help, but I think is more. So why am I there? I have panic attacks when I see his call, I cry most times, self esteem is bad now, I am depressed and I have lost respect for him as well as myself. I want to just walk away with out saying anything, I can’t talk to him about anything because I am afraid it will go to the other woman.