Wow. I have almost the EXACT same situation going on except that the guy I met on myspace over a year ago is NOT married, I AM. My husband knows that I'm in love with this other man and we're going through a seperation. (The state I live in at the moment requires a one year legal seperation before you can file for divorce...) My husband and I have been together for 12 years, since I was 16. The new guy has told me that he wants to be with me, that he loves me, etc.
In your case I would suggest you bringing it up to him. Seriously. Do NOT be afraid to just ask him how he feels! If you don't know if this man loves you, don't concern yourself with the "involvement" with him. You can't continue loving and wanting to be with someone if you don't know if it will ever go anywhere. ASK HIM.