I agree kiwi.
For me personally, a much regretted drunken mistake in the past isn't necessarily a deal breaker.
I once came v close to being the drunken mistake maker myself, and what it did was it wised me up, made my appreciate DP more and made me realise how stupid it would be to risk everything.
But with just a nudge more persuasion I could have made that mistake. And I know that I love my DP 100% and want to be with him 100%, but life can throw us challenges can't it.
I wouldn't throw away a brilliant, long term relationship becuase of a one night stand. Of course, it would be much easier if I didn't know and didn't have to make that call in the first place.
Also, my relationship with DP has grown over the years. If he cheated on me now in any way shape or form I would be utterly horrified. But if he had done it way back when, I'm not excusing it, but things weren't so solid then anyway and we didn't have a long term plan. I wuold have been upset at the time but I don't need to hear about it now.
Everybody is different, but for me personally it isn't an immediate sacking offence. I think each case has to be taken on it's own 'merit' for want of a better term.