I stretched the truth, should I tell him?

We've been together for only 2 months. We are both gay men. About three weeks into our relationship I made out with and groped a girl at a party while drunk, but didn't get any sexual satisfaction out of it. I don't know why I did it, but it was just something to do I guess. I didn't do it to cheat. I never intended on having sex with her.

I told him I kissed her and pulled away. I didn't tell him I made out with and groped her. I did pull away, but only after a little while.

Now the guilt is eating me from the inside out, and I feel like I have to tell him. I made a mistake that was out of character, and I learned from that mistake. I know I'll never do it again, I like him too much at this point, but I wasn't sure whether I wanted to be with him then or not.

I have friends who say it isn't worth telling him and hurting him again as I'm just filling in details that don't need to be filled in.

I have friends saying that I should tell him because he deserves to know.

TLDR: We are a gay couple. I made out with and groped a girl at a party and then pulled away, but only told him I kissed her and then pulled away. Do I tell him, or just let it go?