1- Know that the presence of homosexual feelings is not haram. Acting on those feelings and engaging in homosexual acts is haram. Try to protect yourself from any homosexual acts, even if it’s not easy. Resist your urges and Allah will reward you for that.
2- As for this girl, if you really cannot feel any attraction towards her, and you believe you won’t be able to consummate the marriage with her, then don’t marry her. As you said, she will become miserable. Don’t tell your parents you have homosexual feelings (if they don’t know), and just come up with an excuse to not marry the girl.
3- Don’t give up. Keep praying to Allah and try seeking different kinds of therapy to avoid any homosexual practices.