One can handle situations such as getting asked to study for an exam over dinner with warmth, as well. One just says, Thanks so much for asking, but I study better at home.
I assume the OP is not dorming at the college, just commuting. Being a commuter makes it quite easy to take classes, do what work you have to, be nice to people, and then go home. One doesn’t have to actively participate in social gatherings, since one is usually not there in the evenings when they happen.
Even if one is dorming, there are quite a few schools that have clusters of frum kids who spend their time together, and not in general campus social life. Some have active batei medrash that have ongoing shiurim and chavrusas.
As far as Mod-80’s concern that one’s eternal life is at stake, why does being rude not also put one’s eternal life at stake? We know that even though arayos is one of the big three, yet one who says I will let a woman drown, rather than carrying her to safety is a chosid shoteh. Bein adam lachaveiro is just as important to one’s eternal life, if not more so. See Rosh on first page of meseches Peya in the big shas. He says that the RBSH gets more nachas from ben adam lachaveiro than ben adam lamakom.