Is it wrong to have feelings for my friend's brother? Should I do something about it?

Hello :)

A really close friend of mine has an extremely lovely older brother. He’s very shy, but very sweet, and the three of us have had dinner several times. I’m massively attracted to him, but have very little experience with dating and I don’t know what to do. I’m 24 and he is in his thirties.

This will sound juvenile, but I’m trying to decide whether or not to add him on facebook. Would that be too forward? I don’t really “do” forward, and I don’t want to create an awkward situation. But it’s not a big deal, right?

We are both very shy, but I just can’t stop thinking about him. I can’t talk to my friend about it yet, and I don’t want to make a fool of myself. He works a lot. Should I wait for awhile and see how things progress? Or go the “add on facebook” route? I just don’t want to come across as the “little sister’s friend”.. :S

Thank you for your input xox