I really like the idea and concept of polyamory but I'm scared that if I try it and decide I'd rather go back to being exclusive with my original partner that it'll be too unfair. Is that normal or is that being selfish?
You’ve set up a false dichotomy in your question, there - that is both normal and selfish. It is really common for monogamous couples to try “opening up” their relationship, decide that didn’t work for them, and “close it back up.”
In theory, this is fine - it’s totally okay to try things and decide you don’t like them. That is, in fact, the point of trying things. You’re not obligated to do something forever just because you wanted to try it.
But in reality, this creates a lot of pain and heartbreak for the other people involved. Imagine if someone started dating you, and then, for a reason that you have zero control over, on the whims of someone else, just dropped you. It hurts! This pattern is often referred to as “couples privilege” in the polyamorous community.
That’s not to say that it can’t or shouldn’t be done. Just that you should be careful, self-aware, and go into it with very clear, honest, open terms and expectations. Do as much self-work as possible in the beginning, unpack your own baggage, get your own house in order. Talk with your partner about best and worse case scenarios. Daydream together about what you’d like. Strategize together about meeting needs.
If you do decide to take this step, make sure anyone you date knows that your relationship with your partner takes priority and may ultimately be a threat. Be patient about the fact that you’ll have a hard time finding someone to date on those terms. Consider starting out with something casual, identified as a fling or no-strings-attached arrangement. Be as gentle and giving as possible with any other person you date or sleep with. Keep them informed about where you are emotionally, and give them space to express where they are.
Or, you could realize that you’re just not at a point yet where you trust yourself to be healthy in any potential polyamorous relationship. If you feel that your concern about protecting your existing relationship will overshadow your ability to be flexible and healthy in another relationship, it’s totally okay to decide that that takes priority, and you’re not ready to try polyamory right now.