There is this girl in a couple of my classes in college. She finds many ways to relate things to me by trying to volunteer me or any excuse she could find to say my name. She made lots of eye contact and laughed at most anything I said. I did some push pull and she touched me a couple times. One day after class, I complimented her and it was no big deal. I just said it then kept talking but it seems like after that day, she stopped doing all the other things I described. She is still friendly but it's toned way down. She has a boyfriend that she has been with for 3 years.

I have problems getting past this because last time a girl told me she a bf, I told her "That's great! He can make us dinner sometime." She told her bf and then he came to my workplace and tried to intimidate me.

Why would the girl in my class start acting differently all of the sudden?

It's quite obviously a reaction to the compliment you gave her (unless there are details you are missing). How did she react to the compliment? In my experience it's not a good idea to just have a compliment in the middle of a sentence, it tends to add a sense of anxiety in the girl for some reason, though obviously it depends on the situation. More details would help.

_________________
Your momma's so fat when she walked past the TV she was going to the kitchen to get cake 'cos she's fat.

Well cerin, this type of stuff does happen, and it may or may not have anything to do with you what so ever. Maybe her and her boyfriend are fighting and she is in a bad mood....or maybe they are getting along. In my experience, don't even bother with girls who have boyfriends, especially if is a girl in your class. Not for moral reasons or anything like that necissarily, but the effort doesn't equal the value more often than not.

Don't analyze this too much, it is a waste of time. Just play it cool, initiate her less and she will either come back around, or she won't. who cares. There are plenty other girls to occupy your thoughts instead of some girl with a boyfriend sending you mixed signals.

I love your response to the girl that had a boyfriend. That is the kind of stuff that makes a good story. Now go hit on some single girls haha!

_________________
The Bachelor's Code by Tyler. Check it out...
http://www.thebachelorscode.com/

I know I shouldn't have but I felt she was into me and I complimented her smile.
I told her she has a nice smile blah blah w/e

She said: "I do?" as if I were talking about someone else. Big emphasis on the "I" so she acted like I was saying someone else had a nice smile.

It didn't seem like a big deal.
She said "Thanks" then I moved the conversation to something else. We talked for a couple minutes while we walked down from the top floor and outside where we said bye.

She started flirting with other guys more in addition to leaving me out.

I haven't really approached girls cold. I talk to them where it's convenient which may be a problem. Places like in class, at work (retail store). This girl pointed out to me that we had two of the same classes together. I didn't even notice but I'm pretty sure she saw me talking to another hottie in communications class.

I've met quite a few girls but not as much as I should. NONE of the girls I've met have been single and it's not like "I'm gonna fake a bf to get you away" type thing. One girl didn't tell me about her bf and she gave me her number but just made up shit about her phone being broken/ her being busy.

I do not drink and never have so I don't go to a lot of parties.