Is it possible to develop feelings for someone if you have feelings for someone else?

Is it possible? I had extremely strong feelings for a friend which weren't returned and have been working on getting rid of them for the past month or so but they are obviously still there, just not as intense as before.

Anyway, I've been talking to a guy casually (he knows my situation in brief) and I wouldn't get into anything serious until my feelings for the other guy were gone. But is it possible to develop feelings for the guy I'm talking to if the other guy is still on my mind? The last thing I want to do is lead him on. He's really nice and we get on well, and I would really like to get to know him but I'm worried my other feelings would prevent me from getting into a relationship