Don't punish rules broken. That is not good karma. Either it was too much for you and you end the relationship, and you forgive and work throgh it together.
There are phones. If you are uncertain, call or text and ask. If you are still uncertain, don't do it. Limit your drinking at parties, since more than a couple of drinks makes for bad decition making and possably rules broken. If you mess up, apopologigize and allow the other person to feel hurt for some time, and work on re-building the trust. Use a condom. Also, me and my husband has a "try not to fuck them in the same night as you meet them"-rule, but again: there are phones.