Wtf, just forget about it. What's the point to bring this up now? Then what? A couple more years and you remember another little dirty detail from that night and put her through this all over again? You had your chance to be honest. Those are past waters now. Bringing this up again would just be a self serving way of using her to clear up your conscience.

Water under the bridge. There's no point in telling, all you'd do is hurt her yet again, and potentially jeopardize everything.

Nothing happened after all, so put it down as a near miss and make sure that's not happening again in the future. If you can't handle alcohol, leave it be.

Let sleeping dogs lie...

So I told her almost all of it (and it was very painfull for us). Except the fact that I proposed in a separate room to engage in sexual stuff with a couple. They refused but I still did propose. (This feels very very wrong for me)

I don't see how bringing it up now changes anything, but if it's really eating you up inside then maybe it's better to tell your partner. Otherwise let it go. You already confessed to stuff you did that evening. I don't see how propositioning a couple for a threesome and being turned down is somehow "worse" than actually making out with people.

Own it. You already came clean. Move past it. You had your moment. Don't revisit the same issue again. It's overly dramatic for the relationship.

It's never too late to tell the truth.

On the other hand, are you telling her something that will hurt her to make yourself feel better? Sometimes a secret is a kindness.

This doesn't sound like one of those times, though. She should have all the information and be able to make the decision for herself.

I would sit her down, and tell her exactly what you just told us. Tell her what happened, and tell her it was weighing on your conscience that you propositioned a couple at the party.

If it were me, and I already knew about the hook-ups, and I had already gotten past it, the new information wouldn't change anything for me. I would be more hurt that you kept a secret, but I think I would understand. Hard to say how she will take it, though.

Are you doing it for your own sake, or for the relationship?

I think maybe you should approach this from a different angle. Rather than just to "get it off your chest," I think you should approach this as a problem to be solved.

We're all human. We all do things we wish we didn't. To be adults means to recognize under what conditions we make these bad decisions, and rather than just try to "do better," you should work to remove those conditions. What I mean by that is, if you were to get drunk at a party today, what's to stop you from making that same bad decision? Have you stopped going to parties with the kinds of people you would proposition like that? Have you stopped drinking alcohol so you wouldn't get drunk in the first place? Or have you not changed anything at all, and those same conditions could reasonably come up in your life again today?

If the answer is "these conditions can't come up again because I've already made life changes to prevent them," then great! No need to bring it up with the girlfriend, because it no longer represents a future threat to the relationship. You are no longer the person who did those things because you have made a change in yourself that wasn't present back then.

If the answer is "nothing in my life has changed to prevent this from being a future problem," then you may (emphasis on may) want to bring it up as a problem to solve as a couple. Consider telling her about what you did in the context of asking for her help preventing that from happening again. Talk about what you think led to that situation and brainstorm things you can work on changing that she can help with. Maybe you only go to parties together and she helps keep track of your drinks? Maybe you stop going to parties and come up with other activities to socialize with friends (hiking, mountain biking, fencing, pottery, poetry writing, Warhammer 40k figurine painting; the limit is your imagination)?

I don't know you, so I can't suggest changes that I think will work for you, but she does. The hardest part is that you have to legitimately want to change and you have to put in a good faith effort to make those changes. To make this work, you will have to sacrifice something, maybe sometime you really like doing. But it ultimately won't be for her or even for your relationship. It will be to make yourself a better person, one who works at having a healthy relationship with your significant other.

You need to learn how to forgive yourself first. Do you think a minor detail like that would have been something that would have convinced your partner to leave you? It sounds like you two worked everything out and built up that trust again. Bringing it up now only serves to clear your own conscience at the cost of opening up old wounds.

Look, you acknowledge that you made a mistake, you've atoned for the bad things that you've done and made amends with your partner, and you've found a blissful happiness. It's time to let that baggage go and forget the past. It won't be easy, but the first step is to realize that everybody is fallible and that sometimes we make mistakes and we can't always rely on having our guilt absolved by another.

Honesty is always the best policy

I don't think you are ready for a relationship