To anyone reading this that is super frustrated about them breaking up or not getting back together let me tell you a thing about being apart like that.
It sucks really bad! He was being faithful by not going out with that girl to the beach because that would of definitely been inappropriate for sure when in a loving relationship.
But being lonely sucks. It sucks a lot. Without your sweethearts touch, without their embrace it can become extremely lonely. And it's not like you can go and get it from any other person! Otherwise you would be a cheater and that is no way to have a healthy and functional relationship.
In all reality she could of left her music career to be with him, but he was right to not ask her of that. It's the ultimate catch 22. She may of come to resent him if he asked her to drop her career and be a stay at home wife. But she did not also want to leave her career because it made her happy.
The ending though shows us that they both still remember the relationship and how special it was. It had its own kind of special, you will feel this on your life I promise!
Even though he did move on and marry the girl who invited him to the beach. Believe me when I say that he probably thought many many a night what his life would of been with her. It was only after MCF matured even more that she realized she gave up the person who gave her meaning in life, and sadly this isn't something you learn till you either get some revalation or you lose the thing that mattered most.
If you have gotten this far in my comment I just want to remind you of this. Things like career and social status and your own pride as sooo fleeting. But when the sun sets over the horizon, the love that you share with that special someone is the only thing that will matter.