Constantly asking why i have friends

This might seem a strange one or it's more common than I realise, either way, I'd be grateful for any answers.

Anyways, I'm 51 yrs old, recently diagnosed as autistic as mentioned here previously and trying to get to grips with things, like alexithymia and autism inertia but thats another story.

For 40 odd years of my life, I never truly had friends, I had acquaintances that lasted a couple of years and petered out, for the 1st time, I now have genuine friends, I have 6 friends that have been part of my 40's and now in my 50's, 13 years in total, 2 of them are from a very famous thrash metal band and attended my 50th birthday party.

I keep questioning why they are friends with me, what have I done to get such brilliant and solid friendships, I jokingly say it's because they are 500 miles away, just recently, one of them said they were coming up to Scotland and invited me to come up and spend the night with them, I must admit, I cried, He and his wife have done this a few times before but since my autism diagnosis, I found myself being more weepy than usual.

Is it normal to be constantly questioning yourself why you have real friends?