Need Some Advice

Ok.. class ended 2 days ago..HIS class, I've developed a huge crush on my astronomy professor. First day of class I knew I was in trouble, Astronomy has always been my passion, I plan to major in Astronomy/Astrophysics. He's definitely attractive but I didn't really think I'd ever pursue anything. Well i ended up adding him on facebook after awhile, and learned more, he's not married, does have a g/f but eh doesn't seem too serious. He's into everything that I am, rpg games, watch same tv shows, he just seems so perfect. I actually got up the courage and messaged him a week ago even though I was still in his class, all I said was "you're kind of amazing" he responded by saying "thank you, are you ready for the final on tuesday?" which i said something cute and he put a "=p" well classes are over now, and im wondering if i should say more? I know he answered kinda professionally, but at that time I was still in his class, so he kind of had to, right? Is this inappropriate? I can't help how I feel.

Forgot to add, I'm 25, he's 35.