I had a guy friend for years, we were very close. One night we cross the line and got intimately involved.?

after the "deed" he invited me over the next night and we had another amazing night together. I was married, but separated at the time, he was single. He told me that he could get use to this,...us being together this way and I told him i would like to see him again. I never heard from him again, and that was nearly 4 years ago. I wished I knew what happened, but I don't. Should I try to contact him after all of this time or no and just let it go?