So, I'm guessing it's a sociology class or a philosophy class. Remember, you can learn ABOUT something without having to submit to that thing. You can learn ABOUT Islam without becoming a Muslim, you can learn ABOUT communism without becoming a Communist, and you can learn ABOUT relativism without becoming a relativist.
Just remember that you are there to LEARN ABOUT, not to LEARN FOR THE PURPOSE OF BECOMING.
And remember, you have the local Catholic community and this forum for support. Don't feel the need to abandon college over this issue yet. One of the most important things you can learn at college is to learn how to entertain ideas without becoming an adherent to them. Learn what your professor has to say about relativism. Learn the history and the rationale he gives you about it. Learn the topics he uses it with. Entertain the notion. But be able to entertain it without becoming beholden to it.
Edited to add:
Also, remember that depending on the cultures you are talking about, many many cultures didn't accept that the Earth went around the Sun either. The first person to even propose it wasn't until about 300 BC ish in Greece, and that never caught on. By the middle of the 1500s, India I believe only had a partially heliocentric model. Medieval Islam certainly hadn't embraced it by 1200 (that's where the Islamic History class I took ended its talk on astronomy). According to this study reported by Reuters,
http://uk.reuters.com/article/2011/...-poll-education-science-idUKTRE71A5B920110211
about 32 % of Russians still think the Sun goes around the Earth, and according to this Gallup poll 20% of Americans think the same
http://www.gallup.com/poll/3742/new-poll-gauges-americans-general-knowledge-levels.aspx
So, while I don't know the context about the 'earth goes around the Sun' comments that were frustrating you earlier, just saying that the idea of the Earth going around the Sun is an example of change isn't necessarily a jab at the Church. (Now, he might have made specific jabs you didn't relate, in which case I'm sorry for this huge off topic edit.)
Metherion