I'm going to break up with my girlfriend after he came out to me as being a guy.
Why do you want to break up with him?
He did that because he wants me to feel sorry for him.
It's reasonable to want to break up with someone if they transition their gender. Otherwise you would be with someone you aren't even attracted to.
I don't want stay with him because he's going to get so much attention with this.
He is not who you met and started dating. It's reasonable to end the relationship.