I think I'm falling for a guy at class

He's so cute (and hot... - you know the type!). Let's call him Bill. Today, while I was going to class I checked on a guy and thought, "omg, he's hot!". Then I realized it was Bill, which was followed by me having butterflies in my stomach.Last time I felt that way I was desperately in love for Jack. That led me to extreme mood cycling and to a psychotic break, and then depression. By a psychotic break, I mean I had Erotomania (in short, I thought Jack was in love with me and that we communicated through signs). Now I'm getting back on track with the help of medication.I'm thinking about Bill a lot lately. I don't think Bill is into me, realistically speaking, I don't even think he's gay. But at the same time, I can't stop fantasizing... Something inside me says "he's gay! Go for it!". The point is I'm afraid I might be getting insane again, despite of the drugs. I can't trust my instincts, given what happened in the past.Oh... I also have a boyfriend. Let's call him Ted. I don't cheat. Never had and never will. (Yes, I like checking out guys. I know, I'm a mess...) Me and Ted are going through a bad phase in our relationship. And I think maybe the fact that I'm falling for Bill has something to do with it.Can you guys say something to me? Any piece of advice?TL;DR: I think I'm falling for Bill. Last time I fell for someone I went insane (truly insane). I'm afraid I'm getting insane again. I think that has to do with me and my current boyfriend going through a bad phase. Any piece of advice?