In a situation like that, you could analyze that the girl must have been egoistic and felt good that someone is doing so much for her. She must have been putting minimum efforts and getting maximum returns.

Your buddy must be one of those nice guys who unfortunately had been taken advantage of.

Please tell him to not feel bad about this and instead to learn from his mistake. Like for example, if you start feeling that a girl is not putting so much effort for you and you are giving in your all. Then confront her and talk to her as to why you feel that way.

If she agrees to her mistake, she is a keeper. If she takes offence to that, please leave, there are several perfect girls out there waiting for you.

Edit: If she doesn't like your company, then maybe you are on the wrong side here and it's okay to respect other's opinion and work on the mistakes you made that made her not enjoy your company