Member Rara Avis
Depends on how much you like to gamble; the overwhelming majority of people are likely to continue “cheating” once it's already happened the first time - in other words, the odds are against him staying true in the future.
Of course, there is the chance he might - and the question you really have to ask yourself (in my opinion) is how important it is for him to be monogamous based on your personal morals (some people don't have large issues with a partner being involved in external sexual affairs). If it's really high on your list and you consider it an extreme breach of trust, then perhaps it's best to move on and find someone who shares the same mindset... take it from someone who's been on both sides of the fence, no one "cheats" who doesn't want to in the first place.
If [you] sleep with someone outside the realms of your accepted relationship, it is because you want to, not because you were forced to "fall in love" with someone else (that's a crock, someone who does that CHOOSES to put themselves in the situation where it can happen, want to avoid it? stay away from the temptation!). Barring rape (which is an obvious exception) - people have sex with other people because they want to - whether they feel remorse for it later or not, there is something in them that needed/wanted that.
Sorry, I ramble. Hope it works best for you – I will comment on one thing that I’m sure you’ve already thought of, but feel compelled to bring up – don’t stay with him because if your daughter. You had a child together and that’s bound to be a hard thing to break up (honestly can’t imagine…) – but basing a relationship on something outside of your direct connection (not the tertiary connection of Freyja) will inevitably fail. If you choose to stay together and “work things out,” you’ll have to accept that a) he’s likely to do it again and b) you will have a lot of work ahead of you to continue making the relationship work.
Just my 32-1/2 cents.