Wow, 18, kudos on knowing yourself so early. At 18, I was still trying to figure out which boy I wanted to kiss first!
Being in a poly relationship should be an equal event. If he's allowed to persue other women then, IMHO, you should be able to pursue your preferences as well.
There should be a level of mutual agreement among partners but, understandably, there will be some forfeits as well, like never eating Chinese food again cause the love of your life hold a huge distain for it. Ok, so maybe Chinese food doesn't equal giving up your preferred partnerships but it was the best analogy I could think of.
Communication of needs is so important. Your needs are important.
I hope you work it all out