Could you please help me?

I was talking to this guy online that was in his 30's and I knew he had a girlfriend. Nevertheless, I continued chatting with him because i didn't want to hurt him because he said he loved me. Him and his girlfriend are still together as far as I know, but i feel like a home wrecker. Can someone please tell me if I'm a horrible person? I just feel so terrible for what I've done! i no longer talk to him by the way. Who's guilty here? Him or me? Oh, he's done this before with multiple women. I guess that makes me stupid.