I've asked my girlfriend to fix her behavioral issues for a long time now and also fix her weight, I plan on breaking up with her.
Why do you want to break up with her over that?
I've found someone who is better suited to my needs.
You should never force someone to change when they physically and emotionally can't, or is just not willing. It seems like you could be the toxic one in the relationship, and it might be better that you leave and do some soul searching.
Dude, I'm doing this for her. I don't love her anymore!
Being so critical toward your partner especially on physical appearance will really upset them. I understand your feeling like you're doing this for her, but this still will make her really upset. You should try to love her for who she is.