Don't take this as me believing you because, believe me, I really don't, but let's talk hypothetically:
There are such things as open relationships and if everyone involved is okay with such a thing, there is honestly no issue in this. Just keep in mind success rate for these types of issues are low and problems do arise quite regularly
If that's not the case, it's also not exactly wrong to be seeing two people at the very start of a relationship which aren't really "officially/formally involved", so long as you do break off with one if things develop witj the other; else it's cheating.
If neither apply, then the obvious applies: be with the person you actually want to be with more. I'm not going to say one where you can dee a future with, as most young relationships aren't really for that - relationships are actually good for teenage development, so long as they aren't overly negative, careless and actually involves attraction. Just ask yourself who you enjoy spending the most time with, who is more memorable when you spend time with them and who actually makes you happier.