introduced them to your children and there was mutual loathing
What decent adult would "loathe" a child?
Could you really give up on 2 years worth of relationship because your partner can't get on with your children?
You needn't give up on it though, just accept that if you want to continue, you should keep the partner separate from the children. It's not brain surgery surely?
My youngest is 4, if it were better that he lived with me only until he was 18, what harm is there in that? My DP told me himself if I ever put him (DP) ahead of DC, it would mean I wasn't the person he thought I was. Because DP is a decent human being who would never "loathe" an innocent child or resent them having needs 
In any case even if you ended the relationship at two years, it's not as if it was wasted time, you'd have had a lovely time together etc but it just didn't work out. Is that really so terrible?
Perhaps it comes down to whether a person can stand the idea of being alone. For me, if a relationship ends, that's fine I'll either find another, or I won't, either way I can find happiness. So I don't wring my hands about whether the relationship "has legs" etc. Just go with it, it works or it doesn't, what's important is the DC surely?