Hi Sheree your post rings a lot of bells for me although I'm in my 30s.
I'm English and have a wonderful friend who is an Afghan man. He's genuinely lovely.
How did we meet and why are we just friends? We dated but it didn't work because of the cultural differences you detail. It was not much different because we were 10-15 years older. Ok, if his friends incidentally bumped into us that was ok but I was still excluded from his home and social life except with western or work friends.
I'm not saying nobody can make such a relationship work but unfortunately, he is struggling to prioritise you at all above the expectations placed upon him by his particular family and culture. These are very different to those from yours as you know and include things like not being able to allow you into his family home, introduce you to everyone in his life, talk about your relationship openly.
This is impacting you in ways that are leaving you feeling diminished and like a secret. This is actually a very damaging way to feel for your mental health. He is placing a lot of blame on you, saying you don't understand his culture. Well actually, I think you do understand a lot of it. It isn't just for you to absorb the differences, he has to play a part in managing them and he isn't doing so.
I'm sorry to see I don't see this as changing much and I would suggest amicably leaving the relationship as I ended up doing. Nobody's culture is right or wrong, but his doesn't have the right to dominate the relationship and your feelings to this extent. Also, if a partner's family are openly disapproving or critical of you, this really affects any relationship unless the partner is fully on board with ignoring them/ defending you.
You're 22. Get out there and have a ball. Not to belittle your maturity or feelings as you sound really tolerant and thoughtful but you should never, ever have to feel like a secret or not good enough/ right because of who you are. You've given it a good go with this guy but don't expect anything to change.