I have a friend who “carried” a relationship like that for 7 years, she started when they were 15 years old, well, I have never seen her happier, it was a life changing decision and she made the right one. I understand how hard can it be to put an end to it, but there’s one thing you can be sure: if you made the right choice, you will be happy alone or with someone else, if you made the wrong choice, nothing is permanent, you could eventually try to get back with him. Now the most important fact is that no one is going to do that for you, you must live your life for yourself and always search for your own happiness, if you current situation isnt providing that, I suggest you tell him goodbye as soon as possible!