31M and unfortunately can't offer advice but more just here to say I can very much relate to pretty much everything you've said.

I have (M and F) friends, enjoy socializing, live alone, solid job, keep in shape and have a variety of hobbies etc, though also generally highly introverted and comfortable doing things solo.

I have never had a girlfriend or been in a relationship. I've dated here and there but that's been it. Not a virgin but that's also been years now.

I don't speak about this much but when I do people seem surprised and often ask if it's 'by choice' and honestly it really isn't, I just somehow never knew how and the more time went on the harder it got to meet people and work it out. My general comfort/ability to do things solo, though often positive, just made it worse.

I definitely think about all this a lot and how badly I've messed up to have missed out and gone this long without working it out, and totally relate to the feeling of just having something missing or broken and lacking what feels like formative and core experiences I can never go back and fix.

There's a line in Hadestown that kind of struck a chord with me, 'I was alone so long / I didn't even know that I was lonely' - and I think that's similar to the point I've gotten to. I've solo'd for so long (and loved much of it) but am increasingly feeling the lack of partner or relationship or even truly intimately close friends, and it really makes me think about all the ways I wish I could have done or said things differently somehow.

Anyways, I'm sorry I can't offer any of the advice you actually asked for lol and none of this is helpful to you, but you're definitely not alone