I won't tell you what you should do, but will share with you what happend with me and maybe that will help. Same type of story, I'm gay and going to parties with a bunch of straight people. Same type of guy, straight with girlfriend, but some guys hanging with the guys and the girls together off doing their thing. Well this straight guy Jose "with a girlfirend" use to do the same thing. He always talked to me, gave me attention, but when he got buzzed, things would go a little further. He use to touch me a lot, make sexual comments, grab my ass, touch me, etc. He always did it in a joking manner the group of us always laughed. But I was very attracted to the guy and when we made eye contact, I always felt like there was more there than just messing around to be funny, I felt like he was into me, but never did anything, because well he was straight and although I am straight acting, I am gay, and he had a girlfriend, and other "very gay" guys he never even paid them any attention. It got to the point that after several weeks and several parties, I was looking forward to the attention from him and always wanting him to give me more and take it to the next level...... I was falling for him!!!
So I talked to a friend, "girl" that also attended the parties and explained to her that this guy was really making me hot for him every time he touched me or talked to me or started "messing around" with me. She said that he was prob. interested/curious but just didn't know how else to say it or show it, and when he gets buzzed, he feels more comfortable. That I should get him alone and see if he would still be the same way, that way I would know if he was just trying to be funny in front of others or interested in me. So I got my chance a couple weeks after. We were at a friends house party and were running low on beer. We needed more from the garage to be brought in the house. So I said I would go out and get it and asked this guy "Jose" to help me.... The two of us went out to the garage alone. I went out he followed, we were chatting about what ever, I walked over to the fridge. opened the door and as I started to bend over to get the beer, I said "Just because my ass is up in the air in front of you does not mean I expect you to mount me" and kind of laughed. He took the bait and came up close behind me and placed his hands on my hips and broght his crotch up to my ass and strarted rubbing me and making the fucking motions...... Bingo, no one around to laugh, so I started to push my ass back and talk dirty to him telling him to give it to me and make me feel it, I want it so bad, all of which I was saying in that way that if things were only a joke by him, I could say the same "oh I was only joking too". But the more I talked dirty to him the more he seemed to get into it and his hands went from my hips to my ass, as he started grabbing and then up to my chest so I stood up and leaned back into him and grabbed his hands/arms and wrapped them around me and leaned my head back on his shoulder and he was rubbing up against me hard and holding me tight running his hands all over my upper body. But he never let them go further down past my waist, so I moved one of my hands back and grabbed his head and brought his lips to my neck and he started kissing my neck and my other hand grabbed his hand and brought it down to my hard cock and he touched massaged and grabbed at my hard cock through my pants, and after only a minute I turned around in his arms and went for it my hands on him, us kissing, my hands going up under his shirt to his chest he did the same, my hands on his hard cock, he did the same, me undoing his pants, he doing the same, pants open cocks out each of us strocking each other, I raised his shirt and kissing my way down his chest and across his stomach and blew him right there in the garage. As soon as he blew his load, I stood up and he kissed me again, and said he wanted to "do that to me" and down he went. After I blew my load he stood up and again holding me kissing me and telling me that was great and he wanted to do it again. I told him to get dressed before we got caught by someone and we could "make a run" to the store to get some more beer together. So we took off a few mintues later and he ended up fucking me in my car that same night.
So I guess my point is get him alone and see if the "game" is still the same.
Good luck and hope this helps give you an idea or two....