How do I tell my son he has Asperger's?

I can't give any useful pointers about that - but whatever you do, do tell him whenever you can.  I once worked with an Aspie whose parents decided not to tell him of his diagnosis (when 6) because they didn't want him to grow up with a feeling of being different.  When he finally found out, in his 20s, he was hugely resentful towards them for the grief he'd suffered at school.  Your son is coming up to that crucial age, too, when he'll be starting in with secondary education.  I'd say he needs to know before that time.

I can't give any useful pointers about that - but whatever you do, do tell him whenever you can.  I once worked with an Aspie whose parents decided not to tell him of his diagnosis (when 6) because they didn't want him to grow up with a feeling of being different.  When he finally found out, in his 20s, he was hugely resentful towards them for the grief he'd suffered at school.  Your son is coming up to that crucial age, too, when he'll be starting in with secondary education.  I'd say he needs to know before that time.