Boyfriend Texting other woman

If you were with someone for a year and then finding texts messages from him to another woman asking to have sex multiple times up until November which In actual fact she was rejecting his offers! What would you do?

Knowing the Background

My partner had been in a relationship with this woman (in the texts) previously, apparently it was short, being told 4 days anyways I was not told this prior to getting in a relationship that he had only split up with her 3months ago!!! This doesn’t sit well with me. But I have been told men move on quickly!

So when I found those texts messages and confronted him, his words were “that it was out of boredom and that it was wrong and that he was sorry but what if she had accepted those text messages asking for sex would he have done it ? well this is where I have lost trust and you know when you have lost trust in your partner how quickly the relationship can goes downhill..