Once someone's cheated on you then they've ruined it - if not the relationship (well not immediately), then your self-esteem is shot. I've tried pretending this isn't true so many times - but good God when I've forgiven them and they've begged for another chance, I've expected basic courtesy - for them to take great care to never let me feel so bad again.

Of course they never do this, as they don't have the courtesy to end one relationship before starting another. Giving them the benefit of the doubt is exhausting and demeaning...and ultimately you end up in situations like this when people tell you you are being 'crazy.'

I'm recently out of a huge age gap relationship - it gets so boring excusing someone's appalling behaviour because they are young. Having fun is all well and good and understandable (am more than capable of staying out all night myself) but there's no need to be dishonest. I'm your age and I never want to be on the 'hamster wheel' of kids etc. That doesn't mean I'm entitled to lie without consequences - I didn't feel like this when I was 21 or 31 either. In short: you didn't overreact - she has poor moral character and you under-reacted when she cheated with the colleague. You're not the only one to have done this though.