Questions: Flirting

This guy is 33 and I'm 24. He really wants to date me but is too shy to ask. He's my boss. When he has events at his job (college), he invites my younger sister to join, she's 15. He always invites me, and always tells me to bring her. He will occasionally flirt with me, and then he will sit down and get to know her (tell her personal things about himself and bond with her). Is he doing this because he is really into me, or just because it's a sexual thing. I just need to know if he sees it long term or no?

When someone feels a chemistry between them and another person, can it really ever be one sided, or is it really always reciprocated (simple logic would dictate that it is always reciprocated because of the nature of chemistry (or the 'spark' if you will))?

Of course, someone can be an attention whore and flirt with everyone in sight (and this way, it might not be reciprocated, but they DO imitate / emit chemistry, hence the chemistry in this case is faked on one end, but, externally still exists).

What do you think?
Do you believe that a 'spark' or 'chemistry' can be one sided?

This question was kinda inspired by that show Virgin Territory where a girl thought her local coffee shop's cashier might be also interested in her since he eventually starting remembering her regular order. They even started texting her but when she asked him to get a bite to eat and if they could hang out again he said he had a girlfriend already.

I didn't see that coming esp since they have each others numbers and he even agreed to go have something to eat with her.

Also I've had a similar situation except I never hung out with the guy and barely texted. I think he just wanted to be friends but it was nice that he'd go out of his way to make sure they weren't out of the ingredients needed for my order. Some of the other cashiers remembered my name and order but didn't go out of their way to check the oven when they ran out of my usual bagel.