So if two women, for example, love each other and are committed to long term stable relationships that makes it not a sin? [/quote
Correct.
Jesus messed up when He said that a "man should leave his father and mother and cleave to his wife, and they twain shall be called one flesh."
Not at all. Jesus wasn't trying to define the extent of marriage, nor require all men to marry a woman. He was saying that marriage cannot be disolved by a divorcce.
Jesus repeated in Matthew what God said in the book of Genesis: male with female ONLY.
Neither Genesis nor Jesus' words in Matthew say 'only'. You have added that word.
The Bible also forbids fornication, or sex outside the bonds of marriage.
The bible certainly forbids fornication, but it doesn't define it, nor marriage.
So God forbids two women or two men getting married,
No He hasn't. The bible does not directly address the possibility either way.
and he also forbids them having sex together, both, regardless of whether or not they are in "long-term, loving, committed relationships."
A permanent, loving, committed, faithful, consentual relationship IS marriage.
The only thing they can do is stop being homosexual, and ask God to change them. God can and will do this for the repentant homosexual. God can make them heterosexual...
I know many who have asked him to do this. I know of no reliable evidence that he
ever has. I do know of people who have temporarily managed to convince themselves they have changed but none who have managed to sustain the lie indefinitely.