Let's say for example you pray and engage in daily worship, heck you don't just do it, you like doing it. But then you still occasionally talk to guys in class, you guys sometimes hang out, although there's no feelings or whatever you wann say you do feel a little bad at times.
What is so IMPORTANT , is that you cut off all sins. No matter how small, you should stop. I'm telling you even if you hold no feelings, you either will, or they will, or some drama or another will arise form this friendship, for the sake of Allah leave it.
You don't realise how all these little sins build up, and eventually turn into one big sin. So avoid it, be strict with yourself and don't think 'it's harmless'.