Is my best friend Gay, Bi or just Introverted

Ill try to make this as clear as I can and in Chronological Order my best friend and I have been friends for 14 years during which I've noticed some major personality changes when we both hit puberty we started talking about and chasing girls this was around 6th grade and back then we would do everything together during this time and he had no issues talking or flirting with girls at all but he never went all the way. This was the occurrence until early 10th grade where randomly out of no where he cut himself away from everything it became tough to even get him out of the house he would no longer talk about girls and slowly I became the only close friend left I thought he just evolved to be an introvert who didn't share his business with anyone because he'd always protect his phone from me even though I never attempted to snoop through his phone in all our years as friends and I was just dumbfounded as to why the sudden guard he raised. Also in this time I became the only friend he would even to consider to hang out with keep in mind prior to 10th he was a very social kid. He also never had any reason to have self esteem issues now we reach Senior year and I'm finally able to get him to get out of the house to hang out with someone other then just me and he starts to open up more gain some extra friends and it appears it was just a phase then prom night happens and he tells me about this girl he likes they dance and kiss I assumed they would start dating because I know her she told me she liked him to. This was not to be though because he backed out of everything and nothing had happened to ruin the relationship speaking with both parties and he then starts to retreat back to his hermit phase with me being the only friend again graduation he decides hes going to sign up for the Air Force after graduation and we spend more time together and as his departure nears his Mom seeks me out to ask this one question " Has he ever had a girl friend hes never brought anyone home" now i'm very confused because his family is close and for her to seek me out for this really sparked a hunch . Fast forward to this past month where I actually came out to him he told me he had a hunch which leaves me scratching my head because of everyone that I've told some of which are closer then him NONE of them had even the slightest clue and when I told him none of the others did how did you know? no reply . 2 nights ago I finally decided to put this to rest and ask him "Hey can I sincerely ask you a question as your best friend and can you not take any offense to it?"and he just didn't respond to that ether which is very uncharacteristic of him to ignore me so i'm still left here in the dark wondering.

 

That's what worries me that something fell out or something happened and now he has issues locked away over the past 2 year I've been reminding him I'm here and will always be here and that we've known each other since we were kids and he's opened slightly more.

It's really tough to string out the entirety of the past 6 years of our friendship in a few paragraphs and Ive been trying to think what possibly could've happened to transform him and the most likely senerio I see is him suppressing his sexuality and I look at my own story and it's very plausible that's what's happening But until he says something I have no idea. As of late I've turned the heat up on him to draw out whatever the issue may be and I hope it reveals itself to me soon because there is something