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As for the infatuation itself, you said yourself you were in a bit of a rut. The easiest way out of a rut, hands down, is to fantasize. It just so happened this guy popped up when you were ready to start fantasizing. There's no shame in it - he served as a coping mechanism when you needed it, and now that you don't, you've moved on to an active dating life of your own.
I say you have nothing to be ashamed of.
The only thing we can to with the past ... is learn from it.
You may make him feel comfortable, so he talks to you. He may see you as an older sister, or auntie type figure. That allows him to blossom in your company. It doesn't mean he's going to be infatuated with you ever - and most importantly, it doesn't mean he thinks you're infatuated with him. He may think that - but then again, it most likely hasn't entered his head.
He just feels like you care about him on some level, and he basks in that. it's a good thing. He just feels safe with you, that's all. :)