Need some help dealing with an issue...

I've been struggling recently with the Bible's stance on homosexuality. I have always been a strong (straight) Christian but this is really vexing me.

Leviticus 18:22

You shall not lie with a male as one lies with a female; it is an abomination.

Why? What reason is there that God could possibly have for preventing two people who love each other from being together? If I was told by the Bible that my relationship with my girlfriend was wrong I don’t think I could deal with it. I have no idea how homosexual Christians are supposed to just accept that they have to not love the person in their life that means the most to them.