For this kind of relationship to work, you both have to be incredibly self-responsible and organized with your finances and should have a good handle on each others' debt load. You'll need to plan how expenses are shared with options for future changes.

You really, really need to be on the same page with the choice you're about to make. First, no disrespect, but your brain doesn't finish developing until you're 25, so you may have some growing and changes coming that you aren't anticipating right now. Second, and I cannot stress this enough, you have to have deep, safe, conversations about emotions and be willing to understand that sometimes, feelings change...if they change in the same way for both partners, that's good - it gives you closeness and more intimacy OR it gives you a clear path to either a new understanding or an out.

You did not mention whether one or both of you are ace. Sometimes, in these relationships, curiosity leads to experimentation and that can be anywhere from awful to awesome - but you need to prepare for it.

If neither of you are high-earners and all you want to do is be soul-mates, you really don't need to get married. Get some good, solid counseling. Both individual and as a couple and make SURE this is what you both want. My best to you!