What were you talking about before he suddenly went cold and distant? There will be a reason for it, the hard part is just finding out exactly what it is. Either that or he's scared of getting too close for whatever personal reason he has.
Don't always assume it's your fault, people have their own oddities. He could even be going through something you don't even know about and stressed with something personal.
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The term Aspergers is no longer officially used in the UK - it is now regarded as High Functioning Autism.