can a relationship move past it?

[OutOutLetItAllOut]

hi,
me n oh have been married 7 yrs, and have 3 kids.
i found out a few weeks ago that he kissed someone else.
i found out due to the fact that she said thanks for a lift he gave her, that he tried to hide, so i hacked his hotmail, and sent her a message pretending to be him, and she gave me the details i needed.
it was 1 kiss, which i think he regretted.
and tbh, was more to do with the fact we are / were havin issues anyway.
but how do i move past it and start to trust again?

start off with him admitting it and explaining why that course of action was OK.

Is he going to be coming into contact with this person again? is this just the begining of something and if so it needs to be stopped now before it goes any further.

he will be seeing her again.
they work together.
he has admitted that it was totally wrong, has answered any questions i have asked, has not got defensive or angry, has taken full responsibility.
said he did it cause he was lonely.