The worst thing about being 18 is that older people tell you don't know anything yet and that all your problems are because you are young, which belittles and minimizes your feelings.
The problem is, EVERYONE who used to be 18 and is now much has realized that, indeed, we DID NOT KNOW ANYTHING when we were 18.
(This seems pretty obvious now that I'm 30, but not when I was 18. Everything was agonizing at 18, for no particular reason).
Being 18 and in college is for figuring things out. Things about yourself, your views on the world, and how/why/what you want to date.
So your problems seem mostly like normal college problems, regardless of mono/poly issues. It is normal to try to continue a relationship with a high school boyfriend who is at another school, and it is normal to have difficulty doing that.
It's normal to have difficulty with long-distance relationships, and with poly relationships, and with mono/poly relationships, no matter what age you are. But because you are 18 and (I assume) less than one month into your first semester of college, the advice I will give you is not the same I would give if you were 28 or 38.
You're having the questions you have because you don't know yourself yet. You don't yet know if long-distance relationships aren't right for you. You don't yet know if polyamory isn't right for you. You don't yet know if your boyfriend is right for you, or if someone is would be more right for you.
There isn't any way to figure all this out except by trying things, being open-minded, being honest, and accepting that getting hurt is something that happens to everyone at any age, and that you will recover from whatever happens.
Everyone says being young is awesome, but I didn't think so. I absolutely HATED being 18. I hated not knowing myself, not knowing what I wanted, not being sure of anything, feeling like everything was the end of the world, feeling like no one understood me. My college years were NOT AT ALL the best years of my life. (And there's no reason they have to be).
What you should be doing right now is ENJOYING COLLEGE. Not fretting about your boyfriend dating girls on OK Cupid, not pining for an unrequited love [who you've known for less than a month?], not agonizing about whether or not you are poly.
Make new friends. Flirt with guys in your chem lab. Join new clubs. Figure out what classes you like. Get a part-time job so you can afford to go abroad someday. (Oh, and study every once in a while).
It's definitely a challenge to try to figure out whether to keep seeing your boyfriend. But I don't think that's a poly issue so much as a COLLEGE issue. You'll be having new experiences and meeting new people and becoming a new person. Very few relationships survive that--and the ones that do usually underwent a period of being-broken-up through the college years so that each person can grow on his/her own.
I would suggest you talk to your boyfriend about having a period of not contacting each other (say, for the rest of the semester) so you can each grow without thinking about who he is dating on OK Cupid. But make definite plans to see each other and talk during winter break, so you can decide how you feel about each other and the relationship.
Or, if you've already lost interest in your boyfriend, break up with him.
Then meet a bunch of new people to distract yourself from your unrequited crush. Don't worry about needing to "get over" the crush or beating yourself up for not getting over it. Accept that you're NOT over it. Maybe next year, he'll be single. But in the meanwhile, you need to figure out more about yourself.
Here's the poly issue that you DO have: your friends' unhelpful comments about how you're just delaying a break-up.
I really sympathize with your frustration about your friends' comments. I have been told the same thing, when I was much older than you, and it is really hurtful.
You should try seeking out some poly communities (in real life, I mean, not just here) so you can meet sympathetic people. An open or poly relationship is tough enough even with supportive friends.
And, an open or poly relationship is tough enough for people much older than you. I can't imagine having a poly relationship in high school and early college. Most people just aren't ready, because they don't have enough experience with relationships, with communication, OR WITH THEMSELVES.
Best of luck. Life gets easier--I do promise you that!
Single, straight, female, solo, non-monogamous.