Becoming confident for myself, not others

I'm not really sure where to put this, so I hope it's in the right place.

Short background: I've dealt with self esteem/confidence issues pretty much my whole life. I'm overweight and do not see myself as someone who could be attractive to other people even though I have gone on dates and have been told I'm beautiful. I've always been a giver; making sure others are happy or doing things for them. I've never really taken care of myself or done things where there isn't some sort of external reward. And therein lies my problem.

I'm having a REALLY hard time trying to grasp the concept of becoming confident/happy for myself. Not for anyone else.

Is it really possible to focus on myself and work on changing my outlook on the world and how I see myself if I know there's not going to be some sort of 'reward' at the end? My friend says the reward will be that I'll become happy. My reply to that was "that's all?" But shouldn't that be enough?