With all the work that I have put into my relationship, I am NEVER getting divorced!!! I decided that I was going to convert very early in our relationship and even still, I can't say that I was welcomed with open arms. Interestingly enough, the opposition that we faced only helped to strengthen the bond that my fiance and I have now. (Beginning early in our relationship, we constantly questioned each other to see if this is what we really wanted.) We are sure this is what we want and 75 years from now, when we are old and great :-), that will still be the case.
Negative relationships? Well, that could be dealt with just like with any abusive relationsip (not necessarily interfaith)... therapy, counseling, divorce (if absolutely necessary), and a Rabbi is always someone that a person can seek for guidance.
"If you cry because the sun has set your own tears will not let you see the stars." -Hindu Proverb