<human>: Can you give me the gist of the text in a nutshell?

My [31 F] partner [33 M] of 3 years cheated on me with a mutual friend. They were both drunk and hanging out with other people on the beach. They ended up alone and flirting with each other, then making out. It did not go beyond kissing and he said he stopped it from going further.

He told me the next day and said it was a mistake and would never happen again. I believe it won't, but it did happen. I am worried I will not be able to get over it. I know he was caught in the moment, but I am still hurt and confused. I don't want to give up on things, but I don't really know how to build on something so hurtful.
<bot>: Partner was drunk and ended up making out with a friend.  I would like some advice on how to communicate and move forward with the relationship.