Confused and a bit hurt

I;ll try to keep the background info short and sweet.

I've been friends with a guy for ten years, a year ago we slept together and over time we have turned the situation into a long-distance relationship. At first it was really casual, there was no defined relationship, just assumed. Within the last three months he has referred to me as his girlfriend, asked me to move with him (but I'm not sure if he is serious or joking about this), and has made a real effort to see me more often. We have made plans well into the future for things like seeing one another.

PROBLEM! Before we started dating we were both on an online dating service. I went on to deactivate my account, out of curiosity decided to check his profile. It said he was online at the time. My heart skipped a beat but I figured that by pure coincidence he could have been on there doing the same thing too. Well, I had a constant nagging feeling and I have continued to check his status whenever I don;t hear from him for a couple of days (obsessive, I know) and each time I check, his status says he has been online within the last day.

I'm not sure how to proceed. Is it my fault for not having a real conversation about our relationship with him? It really bothers me that he is still online looking for dates (he has updated his profile recently) but I don;t know how to bring this up. I;m afraid that I could lose any relationship or friendship if I bring it up, but I also can't sit by forever waiting for him to tire of online dating.

How should I bring this up? Should I mention what I saw? Has anyone been in a similar situation? I genuinely love this man, but don't want to do anything to jeopardize this relationship