I'm a non-traditoinal student and my professor and I were kind of flirting throughout the semester. I think he was kind of shy and expected me to be asssertive but I'm too shy myself. I hadn't seen him since December and I'm in his class again. I still like him but I don't know if he's still into me. The problem is that I look young for my age and I think he may be dating another student now who's potentially 20 years younger than he is. It's really difficult being in his classes but I need them for my major, especially because he's kind of acting like a creep now. It's almost like he's saying well you blew it with me. I keep thinking that I should have been more assertive and maybe something would have happened. On the other hand, if he's just out to find someone really young then he's probably a jerk anyway. Still, I can't help being attracted to him. How can I try to test it to see if there still may be any interest?

If there was still some interest you would not have to test anything.
He has moved on to the next young chicky and there will probably be another on after her. That is who he is. Being shy is probably the game he plays.
Get over it and move on.

Let thoughts of him go. He is a fantasy that you shouldn't turn into reality.

A reality check can be looking up your school's policy on professors/teachers/instructors dating students.

Good luck on letting him go and finding someone more suitable for a relationship.

I personally think it's totally inappropriate to date a teacher.

Sure he could pass you if you were failing, but remember he also could fail you because of a bad relationship too.

Stay away from him.

Don't give into these feelings. These attractions come up in colleges and universities too often and you could ruin your educational track if you try and do something about it. Go out to other places, try to meet other people. Sexual attractions for men are different than they are for women, he could be very well attracted to you physically. But that may be it, he might not be interested in a relationship because as you said he could already be having a relationship with someone. Women get emotionally involved, men don't necessarily feel sex to be connected to any long-term plans. So my advice is to look the other way, unfortunately if you find someone attractive it doesn't go away but you have to keep a check on yourself. Good luck!