Sorry this will be long and rambly because I have limited experience in this and no idea what I think or feel and need some advice and I don't want to drip feed.
I'm part of a large social group and everyone is convinced me and one of my best friends have a thing for each other and spend our time either flirting nonstop or bickering like a married couple or teaming up an annoying everyone around us (we both like to wind people up but our friends can't decided if we're more irritating when we're winding each other up or tag teaming and annoying them).
As a result when we go out for meals someone sits between us because if we sit beside each other we poke or prod each other (I am incredibly ticklish and he knows that and I retaliate) but if we sit opposite each other we kick each other (not hard or 'accidently' knock or step on each others toes) because we're children 
.
It amuses our other friends because we also play fight a lot, usually because he's taken my phone or glasses or is just being annoying so I retaliate and poke him or grab him (we may or may not have physically wrestled each other on a camp bed which ended up with me unintentionally straddling him before he picked me up and 'threw' me on the couch before sitting in front of me while I played with his hair and pulled his ears 
) to get whatever it is back or when he's humming or blowing in my ear and I put my hand over his mouth to stop it.
One of our friends also managed to get several pictures of us having a tickle fight because that's the type of thing we do, as well as several pictures of him and I 'looking' at each other to 'prove' he goes 'mushy' when he looks at me, and that I can make eye contact and smile at him at the same time (something autistic people struggle to do with most people).
Doesn't help that I have drunkenly messaged him several times (which he is ridiculously smug and pleased with himself about) talking absolute nonsense but generally very flattering things (which is a double edged sword as I probably do think the things I messaged him, I don't lie so he's decided to take it as gospel but I'm also glad that I haven't ever messaged him anything mean because drunk me is an idiot) and he has tried many times to trick me into calling him a 'pet name' annoyingly I've almost called him it without thinking several times and now that word is an inside joke between us and synonymous with our relationship, (my family know because I mentioned it while drunk and some of my friends are aware of but no one that would say anything because he'd be embarrassed).
Our mutual female friends have also think it's telling that he has commented/complimented me on my pjs (they're themed and match the 'pet name') and as my other friends have pointed out are rather low cut (not intentionally and not something I'd noticed because I just have a rather large chest that makes everything seem low cut or revealing). That he is talking to me about weddings and children (as he has said who he'd want as his best man, groomsmen and bridesmaids and who would I have? Where do I want to get married, would I get married in my home town or the city I live in now, he'd like to get married in the city we're living in as it's where we'd met and the church we attend regularly) his words not mine, and his future career when he is incredibly tight lipped about what he is doing with everyone else.
We've a good relationship that is equal parts teasing and annoying each other, helping each other out when we need it or knocking each other back to earth as we both have issues with over inflated egos at times, but our friends seem to take that all as flirting either intentional or not but flirting nonetheless and because neither of us behave like that with anyone else apparently that is proof we like each other.
Especially considering his rather amusing reaction to our male friend, calling me a jokey nickname that my family have always called me, he was rather jealous and tense but got over it when I pointed out other friends calling me it as well (for reference he does have some rather funny/unusual names he calls me and I often call him bigfoot/sasquatch/yeti or chewy). I've also introduced him to others as such because I'm a delight .
Plus they've also seen/heard him singing to/at me something that either makes me laugh or give him a shove to shut up because he picks delightful placed to do it. (Think the middle of a crowded room filled with our friends, walking backwards through the street while looking at me almost daring me to try and shut him up or over dinner in front of my mother, did not enjoy explaining that he does that sometimes).
TBH I wouldn't say no if he asked but I also love our relationship as it is. It's fun and easy and we are apparently alarmingly alike so we get each other and it's nice to spend time with someone, especially a guy who has an equally loud and domineering personality who isn't alarmed or threatened by a woman with a loud or domineering personality who won't take any crap and who won't take any of my crap either. I have a complex medical history that he and our other friends are aware of but unlike the others who treat me as 'delicate' in lots of ways and panic when I look even slightly ill, he doesn't but when I am ill or having an issue he deals with it without making a fuss then or after.
I had a panic in a crowd so he acted like a human shield and coordinated our other two friends who were there to do the same without saying a word or making an issue out of it, I didn't even tell him I was having an issue but he noticed it minimised the issue and walked me through it another time when I was past the point of dealing with the crowd he just gave me his hand and led me out of it. (None of the helping with my health issues I'd consider flirting just being a good friend, I'd do the same for any of my other friends and I think he would too, he can be an arrogant sod but he's also quite sweet when he thinks no one is looking (I do find the arrogance/aloofness quite attractive generally in men), I also think it has to do with the fact that he can read me very well when he struggles to read others) I have Aspergers Syndrome, which his DF and one of his siblings (and I strongly suspect he is also but undiagnosed) also has so to him there is nothing unusual in my behaviour and that's nice and worth more to me than anything because it's genuine, I'm not the 'token' friend, he doesn't moderate who he is or his expectations of me or my ability because he knows I am capable of anything anyone else (and more if you ask him because someone of my IQ and ability shouldn't have to hide who they are to make everyone else's lives easier, he noticed I moderate my personality and ability especially around my family because they can't handle my personality a lot of the time).