Am I just a booty call?

I’ve been seeing a guy for 6 months. We work together and he doesn’t want anyone to know we are seeing each other. We act as “friends” only at work. We do not go out in public together AT ALL. We only see each other once or twice a week when I go over to his house. I have told him I wanted to end the relationship a few times because I want MORE than to just hide to see each other. When I do this he calls constantly and begs me not to “leave him” but our relationship still does not change. We are both single. I know he loves to flirt with other women - that is his personality. I do not know if he doesn’t really want others to know he is seeing me because he wants to see others, if he is embarrassed to let others know he is seeing me (I’m overweight - need to loose around 40 to 45 lbs), or if he has a “significant other” that he is very good at hiding from me and everyone else. He tells me he “cares” about me and does not want to loose me but this does not make sense to me. When I do not get to go see him for whatever reason he tells me he misses/missed me. He told me the reason he doesn’t want people to know at work is because he has been involved with someone at work before and it didn’t work out too well. However he doesn’t ever want to do things together with people who wouldn’t tell anyone at work. I’ve tried talking to him about it and he just says he knows that he doesn’t (or can’t) give me what I WANT but that he doesn’t want to loose me. I’m so confused.