I don't know how to make this long story short, but need to get it off my chest. I've been friends with this guy for nearly two years - we're not super close friends, but we generally have a good time when we see each other. Over a year ago I developed romantic feelings towards him - it was the biggest surprise to me because he's not someone I ever thought I'd have feelings towards. When I first met him there was zero physical attraction - I almost thought of him as the big brother I'd never had. I don't know much about his relationship history, but I do know that he's only had one proper relationship and it was years ago. Given his personality-type, this isn't down to being a player or anything - he's quite extroverted, but immature and has a quirky personality. He seems to flit between being the 'entertainer' and being awkward. He's also nine years older than me. I don't know what or when I developed feelings for him, but sadly there was no turning back.
I've seen him very little over the last year due to life circumstances, but we've met up occasionally within a group of mutual friends. Unfortunately, lately he's been around much more and it's kind of sent all the feelings flooding back. Complications come in the form of another girl in our friendship group likes him and from the way I've observed them together, I think he probably likes her. They have similar taste in music and get along well. I mean, technically, that should be the end of the story, but it isn't. When I first met him he sort of acted a bit aloof and uninterested in me (not relationship-wise, but as a person.) I honestly thought he didn't like me when we first met. But then as the months past he became very warm towards me, sometimes acted flirtatious and we generally had a good time together. This seemed to switch sometime around last year again and he's acted hot and cold towards me ever since. This is the bit that confuses me I guess. Sometimes he can be the sweetest, funniest, loveliest guy and other times he acts like I barely exist. At one point (before I developed feelings for him) I did begin to think he may like me. Now I honestly don't know either way - I go from thinking he has secret feelings for me to thinking he's figured out my feelings for him and is weirded out about it and doesn't know how to act around me. He invited me out to his Birthday celebrations lately and he was the only person I knew there - he greeted me affectionately, but as the night went on he seemed increasingly distant - I appreciate he had friends there who he is closer to than he is to me - I get that; it's cool. But it got to the point where he basically ignored me - he probably said less than twenty words to me all night and weirdly as the night went on and he got drunker and drunker he just ignored me even more. He barely looked at me for the last 3 hours of the night, but he engaged with his other friends (and there weren't many by the end of the night.) Part of me just thinks maybe our personalities don't click and this is disguised in a group setting of mutual friends, but I don't really think that's it - because if we really didn't click we wouldn't get on so well at times. He's extremely extroverted, while I'm more of an ambivert, but I did make an effort with him and got basically no response/effort out of him. I know realistically I should just cut-off the friendship to save my feelings, but we have mutual friends so even if I didn't hang out with him without the others, there would be times I'd end up meeting up with him. On the recent night out I did end up getting with a random guy in front of him - I've never done that in front of him before, and to be honest I didn't do it to make him feel jealous or anything - I just thought why not? Him and his other friends left the room as soon as it happened - I found his friends again quickly afterwards, but he didn't appear again for a while and again didn't look at me or even mention it to me, which I thought weird given that he's normally quite teasing about guy stuff. Again, it may just have been a total coincidence or he was just giving me privacy. Who knows.
I'm basically stuck, because I don't know why his attitude is so changeable towards me - this Birthday night out isn't the first time this has happened. I know I should just ask him some time, but that risks causing trouble where it might not be necessary. At the same time, whenever he does treat me fairly coldly it bothers me and upsets me for a long time. I feel like I'm in this friendship cycle with him of positive-negative - but the vast majority of the time my friendship with him just makes me feel sad. I always thought he was pretty naive when it comes to figuring out women's feelings for him (like I said, he basically has zero relationship experience and from what I've seen he generally doesn't seem to "get" women very well), but a comment he made whilst drunk (about someone else, not me) made me think he's maybe not as oblivious as I'd previously thought. Basically, I value the friendship at its good points. I don't want him to see me as some weird girl desperate for his attention, because deep down that's not what I am - I get that we'll probably never have anything beyond platonic friendship, though I can't help my feelings. I wish I could. I just don't appreciate the cold treatment that I sometimes get, which seems to have no rhyme or rhythm.
I know guys on here aren't mind-readers, but I honestly feel pretty miserable about all of this. I would feel the same about the hot-cold if I had totally platonic feelings towards him, but I guess the fact that I don't gives it some extra kick.
Any advice/thoughts would be appreciated.