My answer is strictly hypothetical, as I am married.
My biggest deal-breakers would be...
If I found out that he had lied about something major. Example: I ask him if he has kids and he says no, then I find out he's sending child support to some chick he knocked up a few years back. If he's lying about that, what else might he be lying about?
If he were married (or otherwise in a committed relationship) and I was "the other woman".
I'm not so particular about religion (as long as he's not a devil worshipper or anything

), but he must support my choice to raise any children I may have as Jews.
ISPP, what a sad story.