You know, Innis -
One thing you need to take into account. EVEN IF he came running back tomorrow, said it was all a big mistake, etc etc - is this a man you can trust around your 12 year old daughter?

I know you said their relationship was very good up until this point, and I'm not trying to accuse him of anything right now. But imagine, if you will, moving back in with him, your daughter going through puberty - is a man who has demonstrated the ability to develop this level of erratic behavior, one who should be trusted around a teenage stepdaughter?

If it were up to me, I'd say, thank god you only had 3 years into it, pick yourself up and move on (and maybe don't move in with another man until your daughter is grown). But if you do stick around and eventually take him back - I still wouldn't live with him for a few years. Let him prove himself.