I said I was sorry so many times and he won't take me back

My boyfriend and I had an amazing relationship, the perfect one, I thought he was the one and I still do, but I slipped up and texted an old friend (who was a gut) and I flirted with him..... I told my now ex but friend I was sorry so many times and I deleted that guy from my life, I never even look at other guy's without thinking about him and no matter how loyal I am he won't forgive me for this m, I've cried over it ever since we broke up and I hate myself for it, I know you guys are older and more mature than me so I'm asking you guys, what do I do?