He was in love with her and didn't want anyone else. She called him a player when she was the one making the rules to her game. He wanted her to be his one and only. Turns out he was her one of many not the only one she was involved with stringing them along.
He forgave her accepted her flaw and all turns out it was not meant to be. Love was his drug addicted and could never get that fix to be satisfied the more he tried she got more distant. He couldn't figure it out trying to understand make sense of it all.
Eventually he walked away learning only he could make himself happy and not leave it in the hands of others. Even though he loved her he wasn't responsible for her happiness. He had to wise up protect his heart since it was being tormented by someone who didn't match how he felt or put forth the same amount of every.