Nope.

From a mans perspective. I have a friend like this [M21] I love him like a brother but he pulls shit like this on every girlfriend he has ever had and it never changes.

You hear stories about it all the time too. Try to find me a success story about a relationship who survived 5 years or more after an affair. You won't. If it has survived theres a good chance they are miserable.

There are literally millions and millions of guys around your age who would not cheat on you. You deserve better. Dump him and leave him. I know it is easier said than done, but the longer you stay the worse it will get.

Find someone who actually loves you enough to care about how you feel.

Heres the bottom line. People who cheat are normally what philosophers would call "System 1 thinkers". They don't think before they act. It would take A LOT MORE THAN A PROMISE to change their behavior. I'm talking about therapy, and lots of practice.

I was in AA for about 2 years of my life. My old sponsor was also apart of SAA (Sex addicts anonymous). He had a girlfriend of 7 years who he cheated on for a solid 4 years out of those 7. Every time he was caught he said something similar to what your boyfriend told you and every time it always led to the same results.

It took over a year of working the 12 steps in an SAA program in order for him to be able to control himself. Along with gaining control, he also became an entirely different person. He had to essentially rewire his brain and perspective on life.

He used to tell me the way he thought while he was cheating and how it differs from his thought process now and let me tell you -- It doesn't change over night.

I hope this helps you with your decision.