How do you let go or if you know you have to for the better of both?

WELL HERES THE DEAL.. I AM WITH A GUY N IM A GUY.. WERE IN A RELATIONSHIP THATS BEEN ON AND OFF FOR A WHILE N THINGS HAVE HAPPENED WITHIN THE LINES THAT MAKE US BE TOGETHER.. BUT THINGS DONT SEEM SO PINK PONNYS AND RAINBOWS.. IT SEEMS LIKE THIS LOVE IS TOXIC N NEEDS TO TAKE A BRAKE TO FIND OUT WHAT WE NEED TO DO.. I LEFT MY FAMILY TO BE WITH HIM.. AND THE THING THAT KILLS ME IS THAT I LEFT IN A BAD TIME.. SEE MY MOM WAS DIAGNOSED WITH BREAST CANCER N I FEEL GUILTY FOR NOT BEING WITH HER IN THESE HARD TIMES.. N I FEEL AS IF I NEED TO CUT THIS RELATIONSHIP THAT I AM QUESTIONING OF LEAVING EVERYDAY I WAKE UP.. BUT I DONT WANT TO HURT THE GUY I AM WITH I JUST WISH HE'D UNDERSTAND WHERE IM COMING FROM.. N I WISH WE CAN BE TOGETHER IN THE NEAR FEATURE.. WHAT DO I DO IN A SITUATION LIKE THIS? ANYONE?