Does anyone have issues respecting boundaries and limits they set for themselves, especially in relationships?

I have set so many limits to myself in my relationship and I always end up breaking  them. The amount of times I've said "I won't put up with this again" or "the next time he does something like this Im leaving".

So far my boyfriend has exhibited signs of drug use, cheating, and most definitely lying. He won't admit any of it but the chances are high. Tonight I made a vow to myself that I would end the relationship. I've reached all my llimits and then some.

Then he sent me a text. "I miss your face" not even particularly romantic. I can feel myself doubting my choice again. "Maybe we should just take a break and try again later. Maybe I shouldn't end it. Maybe we can date casually now. I love him so much."

I know in my heart of hearts that I'm getting the shit end of the stick in this relationship. I should just end it and get it over with. But my love for him/attachment to him, oversteps my boundaries every time. 

How the fuck do I stand up for myself!?!