Where you go for sex isn't relevant. If your roommates know that you are gay or not is VERY relevant. If they don't know you are gay then he could be testing you to see if you are going, to be honest about it.
If he knows you are gay then the options are endless. I've seen/heard/or experienced tons of them. There are lots of straight guys who enjoy an ego building flirt that the know will never go anywhere. They can see if their sex appeal crosses genders and enjoy feeling attractive while being able to claim "I really do like you but I'm just not gay." Ultimately these guys are harmless but they will act like you are their soulmate except you know... you are a dude.
There are also guys that are genuinely trying it on for size to see if they could be with a guy but doing it subtly so they don't get labeled before they are ready. This is especially true if you happen to be one of those gay men that comes off as kind, non-sexually threatening, and drama free. They can "sample" without fear of you pressuring them or telling anyone about what they are doing.
There is also the "any port in a storm" dude who will flirt with you and even have sex with you as long as you don't tell people, make yourself available when he wants, and disappear when he finds a girl he'd rather bang.
The first thing to assess is if your roommate knows about your orientation. The second is how do they view you. If they see you as someone they can flirt and play with and not expect backlash then he maybe playing.
The easiest way to broach the subject is to simply work it into a conversation that you have either never been with a girl or have been and ask him if he has ever been with a guy and let him take it from there.
You've gotten a lot of good insights, but I think these are especially worth noting. A lot of straight guys enjoy a flirt with gay guys, for numerous reasons that mostly do not mean they are interested in pursuing anything with them. The facts that he doesn't know you're gay and that you say he's pretty touchy-feely with his other friends make me think he's all the less likely to mean anything by his behavior.
Just out of curiosity, is he good-looking? If you've got a good-looking blue collar guy walking around the apartment in his briefs and sending you shirtless pics - lucky you!!! I wish I had any advice to give on how to pursue it. I did once have a roommate I fooled around with, but we were both gay and out and so the dynamic was different. Maybe hearing about how we went about it would be helpful.
We'd been living together for the better part of a year and had never had any flirtation. I had never found him particularly attractive or been aware that he'd found me attractive. I'd even told him about an earlier roommate who was a skeezy guy who'd drunkenly and aggressively come onto me, and he'd agreed that was gross and really inappropriate. But, one night, we'd kinda been texting back and forth on sexual topics (I'd been to an appearance of the Warwick Rowers and had come home with a calendar). We were both in our rooms, it was late, and he sent me a text saying something like, "This might be really weird and if so, we can forget I asked but if you'd ever be interested in fooling around, I'd be into it." At first I was taken aback and wished he hadn't asked, but then I got horny and figured, why not? I headed to his room. We had a few more hookups in the next several months we lived together. I made the rule that if anyone wanted to visit, we could only ask via text. That way, there was no awkwardness when we were around each other. It was totally comfortable and if you'd seen us interacting, you'd never have guessed. We had a third roommate who was clueless.
I guess my points are: A) it's possible to have a comfortable NSA situation with a roommate as long as the boundaries are clear from the beginning and B) it's best to go about proposing it in a casual way.
IF you were going to make a move, I'd recommend doing it in the low-pressure way my roommate did. I'd text him one night and say something like "Dude, I'm not sure what your behavior means but if it means you want to try fooling around with a guy, I'd be into it. If not, sorry and we can pretend I never asked." Only you know if the potential fallout would be worth it.
Sorry to be so long-winded. Just my two cents. Take it for what it's worth
