Help plz

I been with my boyfriend for about 4/5 years now.. we break up and are on and off often.. my trust for him is very slim.. everything I try and break up with him it NEVER works ever. Like i believe it’s time to let go of this relationship because he can’t even say why he’s with me. All he says is “because I love you”

Why can’t I let go and break up with him for good? Ughhhhh.... I love him so much but it hurts to be with him @ times but to think of him being with other girls.. it hurts and makes me want to be back with him.