Here's what I would do in your situation, and please keep in mind I'm not advising you to do it, just saying what I would do given my "degree" of polyamory and how much I love my husband.
I'm in the gray area between extreme poly and extreme mono, where I can be satisfied in either kind of relationship. I prefer the freedom of polyamory, but if it meant losing my husband whom I love dearly, I could be perfectly happy and satisfied without it.
I would leave polyamory as a seed in the back of my mind and focus on the here and now. It's a perfect example of "a bird in the hand is worth two of the bush." I wouldn't go out looking for another girl to be polyamorous with, especially if it would mean losing the love of my life. Especially if it's just to "find out" whether polyamory was for me. If I knew for sure and was feeling unsatisfied or trapped in monogamy, that would be different.
For you, it depends entirely on how much you feel that you have to explore polymory, and how much you love your girlfriend. Of course, you're the only person who can answer those questions.
At the risk of sounding pessimistic, if you're young, there's a good chance your relationship with this girl won't last forever. That's just statistics, nothing you've said implies that you're in any immediate danger. You'll have the rest of your life to explore poly. In future relationships, now that you know you're interested, you can bring it up before things get serious.
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker