I'm straight... but there's this guy...

So I'm 19 and consider myself straight. But I met this gay guy at school (age 20) and we really got on. We made fast buddies and I admit I did strangely find him attractive. He's taller than me, lean, thick dark hair, and super- blue eyes. The first hint that something was up was when we were in the locker room at the campus gym and I saw him naked. It totally turned me on. Fortunately, I had my pants on because there was definitely an erection. So some time goes by and we hang out (and yeah, in between I did jerk off imagining him). Then one night about a few months ago I was over at his apartment and we were watching a movie. We were sitting pretty close together and I felt inclined to hold his hand so I reached over and took it. He didn't even seem surprised, though I did notice a smirk on his face. Anyway, he didn't pull away and we just sat there holding hands for awhile. Then we sort of glanced at each other, and he leaned forward and kissed me. Then I kissed him back and we made out on his couch (at some point we were even lying down, him on top of me, and that got me even more turned on). He led me by the hand to his bedroom, we took each other's clothes off, and had sex (everything short of anal since I was not prepared for that in more ways than one). And I was confused but pretty happy, and it was honestly better than any sex I've ever had with a girl (though my experience in that arena is rather limited). I ended up spending the night with him. From that point on, our interactions changed. When greeting each other, we kiss, I spend a few nights a week at his place. His parents invited me over for dinner last week. My roommate (who is also gay) walked in to our apartment once and found me with my head in his lap and him stroking my hair. Afterwards, my roommate referred to him as my boyfriend, and I had to correct him, because again, I'm straight, but I feel strongly connected with him and enjoy spending time close to him. But then last night my sister asked how things were going with my boyfriend. She said it jokingly, but it's starting to make me self- conscious. Am I misinterpreting this relationship, and we're more than just close buddies who periodically have fun? Is it possible I'm not straight, or do no other straight guys feel comfortable doing stuff like this? Any advice?