Holding on is tough. Much tougher than letting go or simply quitting.
Every hello will immediately end with the hardest goodbye as we all knew it. For every beginning, the hardest ending will knock you down, at least for the ones that truly give and take. I'm not good in a relationship, since I doesnt have your experiences, but I know that when it doesnt feel right, YOU'VE GOT TO GET THE HELL OUT!
It's like, if the shoe doesnt fit, get your foot out of it. Its either its too huge or too small. Too huge will make you look like a clown, while if it is to small it will make you look like you're having a constipation and that little black/brown/yellow baby is gonna pop out soon.
So, its either it feels right or not! Follow your heart, listen to your instinct.
Nevertheless, a broken heart will make you even stronger. Just remember who you are! And show it to them!