I'm putting this here and not in gaming as I think it's on-topic as an etiquette issue.
In my spare time I play an MMO which doesn't appeal to a lot of women. Unfortunately this means I get a fair bit of attention which isn't always pleasant. One young man in particular is making me rather uncomfortable:
* he starts private conversations with me 90% of the time I'm playing*, sometimes seconds after log in, even though there are several public channels he can use to talk to me.
* he pushes me to talk to him on Team Speak (VoIP), and if I say no he doesn't take that for an answer and pressures me.
* he occasionally makes overt sexual comments even though he knows I'm married.
* one day I started a voice chat with a guild mate I hadn't spoken to in months, and because I was on team speak to talk to that other guy and not him, he made sad faces at me in the private text chat, told me to 'have fun

' and when I invited him to join us said he 'wouldn't interfere'. Then fifteen minutes later he joined us and said I was mean a couple of times. At that point I logged off voice and told him not to be like that in text chat. He replied that he was sorry he offended me. He said he was trying to be teasing but he's autistic and doesn't always know when he's going too far.
It feels a bit like being in high school but he's twenty five. I've tried dialing back and not responding to him but then he sends me sad emails saying how much he 'misses me'.

Is it wrong of me to find this suffocating and unpleasant? Do autistic people behave like this or is he making excuses? How can I get him to stop it without being rude and making him feel bad? I don't mind chatting with him but not every single day. I also don't appreciate that I can't talk to other people without him joining in or making sad faces at me. Some advice on how to get him to back off would be really nice, please.
ETA:
* To clarify, if we are both logged in he will start a private conversation with me 90% of the time, and as we are in the same time zone he is online almost every time I am on.