Seeing someone, kind of, but slept with someone else...

This is all levels of crazy, I’ve been hooking up/seeing a guy for just under a month-three times we’ve done it. He went away to work for two months three weeks ago, but we’ve maintained daily contact and phone calls....

The other day I got wasted and ended up in bed with someone else, I actually don’t know how I was blackout drunk and can’t remember much from saying we should stop...

Me and the said guy I’ve been seeing/hooking up with haven’t spoke about exclusivity, when he was on the phone to me last night he said he was the only single guy in his group.

Now my question is, do I tell him!? I feel all levels of guilty and like I’ve done him wrong! Am I wrong? I’m not sure

Thanks x