Religion and marriage dont mix
No two religions can ever see eye to eye with each other. There may be some common grounds but at the end of the day, it's a case of those who believe in one's religion are saved and go to heaven, nirvana or whatever, while those who don't, burn in hell.
That's why I learnt a long time ago that the fastest way to lose a (non-believing) friend is to discuss the subject of religion. So let's learn to live together, co-exist as members of the greater community knowing that we have major differences and that these differences will never go away.
Apart from religion, the only other thing which stirs up so much emotions concerns the affairs of the heart. When love is between two individuals of the same religion or set of beliefs, fine. But when the beliefs of two individuals clash, there can only be trouble ahead, and religion will inevitable be sacrificed, by either party or by both.
The possibility of insincere and hypocritical conversion is always there, of course. Then there's the question of what will the children be brought up as. These are critical issues and I am sure that is why the major religions do not encourage interfaith marriages.
My sympathies go out to everyone unfortunate enough to fall in love with someone from another faith.