Help me understand please?

I Was introduced to a guy a few years ago who I learnt is autistic, he lives alone, is fully independent, has a very good job.

He added me on Facebook then started messaging me, I replied however he then started measuring me daily or twice a day. I told him it was too much to which he cut it down for a week or so than it starts again. I don't know what to say next? I don't want to be cruel but neither do I want constant contact. I've tried ignoring him then he gets a bit funny! 

Also to add I swim a lot so he's started to swim. I guess I'm asking what to say to him next, is he a stalker or is this part of his autism? I have no idea.