I’m sorry that you’re upset about his silence. The bottom line is that if a guy is interested in you, he’ll make contact, and if he isn’t, he won’t. I can’t really tell from your post what your history with him is beyond the fact that he’s someone you’ve had sex with, off and on, for two years now. That doesn’t mean he thinks of you as a girlfriend, and it sounds like he’s dating other people beside you because you mentioned your relationship has been “off and on”. You’re probably dating other guys, as well. If you want this to become a monogamous relationship, then I think you have to change your behavior and your outlook and act like the kind of woman he would want to be monogamous with — and if he’s not the kind of guy who’s not looking for monogamy, then understand that, and know that you have different goals.
I hope that helps. Feel free to write with any follow up questions.