It sounds like the problem isn’t so much your masturbating. The problem is that your sex life could use a spark or two (or three!). Just because you’ve “made it clear to him” that your masturbating is not because he’s not good enough in bed, doesn’t mean he believes it. In fact, he doesn’t think he’s good enough, and when he walks in on you masturbating and gets upset about it, I think you’ll agree that he’s not secure in the bedroom with you. Some guys would want to join in — he feels rejected. This rejection he feels is the problem — not your masturbating.
What I suggest you do is to work on communicating and romancing each other. It’s easy to drop the ball after a year of dating, but even the best relationships require work and maintenance. Making sure you keep the romance alive, and the spark in the bedroom, will make him want to be there with you. Give him something to go for. Entice him!
If you need ideas for some creative dates that set the scene for a hot night (or day!), check out my book called Romantic Date Ideas: [url]http://www.askapril.com/relationship-dating-advice/romantic-date-ideas.html[/url].
I hope that helps. Let me know how things go. And I’ll see you @AskAprilcom on Twitter, and on Facebook!