Help a sister out!

Hi I need some major advice. Me and my boyfriend have been dating for just over a year. Now for the past 4 months or so we haven't really been " intimate". I'm concerned because when we talk about it, his explanation is, that he "just doesn't know why he's never in the mood." Now on top of that he does master bate regularly. (Doesn't hide his evidence) I'm worried because this has taken a toll on my self esteem. Not that it was threw the roof before. But I can feel it's slowly but surly taking me down. I also feel that because I'm not as confident in my appearance anymore. That Somehow I'm less attractive to him. So then it's just this horrible circle of dissatisfaction.