For me, I'm waaaay more sociable around people I'm familiar with socializing with. When people join the "cluster" I'm in, they are the minority approaching me and my safe group of friends, which is much better than, say, solitary me trying to engage a group or even one person. If I were him, I might like you very much, but not know how to approach you.
Is it possible you could get to know his group and use that as the foundation for your relationship with him? If not, I'll admit when I was single, my wife made all the moves to make us an item; I was clueless as how to initiate that. He may be also.
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We are not so different from potted plants in that, if given everything we need to be properly nourished, the outcome can be incredibly contrary to when we are not. A flower won't grow in flour, and neither can we.