I think this is going to sound oversimplified. But here goes.
My dealbreakers are smoking (I'm allergic and I have a child), moderate to heavy drinking (I'm expected to trust myself to this person.. I don't want him drunk), and a breach of trust.
Once my trust has been broken once, all bets are off. I don't give my trust easily... and once bitten, twice shy.
Not sure if this is what you were looking for, MissT.
I'm living with a "dominant" partner... so can I answer?
Smoking would be a killer long term for me as well. Any kind of abusive behaivour. And someone who is constantly "needy" -- I've said before that I prefer the "feisty" sub, and that's true of my non-submissive partner as well.