Would I be out of line to ask the guy I'm seeing if he's seeing other people?

So I've been dating this guy for about a month now and I really like him. He has all of the qualities I've been looking for in somebody and every day he keeps finding new ways to flatter me.We went on a very romantic date last night and he had mentioned to me that I make him not want to drink. I asked him why that was and what he meant by it. He explained to me that when he drinks he seeks sex from other men. I didn't need to know that and I wish that he didn't mention that because now I'm always going to wonder what he's doing when he's out drinking. But I applaud him for his honesty.He also mentioned to me that he was seeing somebody and that it didn't work out but they were pretty serious. He said that other guy hit him up that same day wanting to meet up because he was moving. He told me he declined his offer because he respected me and said that if he were in my situation, that would hurt.Fast forward to the end of the night when he was dropping me off at home: we were in his car kissing and saying goodbye and after we kissed I saw him roll his eyes. I asked him why he rolled his eyes and he told me he didn't, but he was looking at his dirty window. I then turned and looked at his window. It had marks all over it like the back of somebody's head had been all over it. I know this from personal experience. I recall him telling me a few weeks ago that he'd just cleaned his windows.Having that been said, I now wonder: is he seeing other guys on the side for sex? Should I ask him this? I understand that he has no obligation to me because he's not my boyfriend, but at the same time I'm not down with double dipping and I'd rather end things now (depending on what he says), rather than later when I'm more emotionally invested. The marks on his window were blatantly obvious as to what they were, I know he had just cleaned his windows (why lie about that) but it contradicts his statement from earlier. So I'm confused.I've been in many situations where I've been with other guys to find out I'm being used in ways like this. To be honest I'm not sure if I'm reading into things too much, or I'm just trying to protect myself because I'm afraid of being hurt again.Any advice is greatly appreciated and thank you for reading all of this. Sorry if it kind of turned into a range toward the end.