When I was 19 and living in a bigger city, I had just officially "come out to myself" and naturally wanted to date a guy, as dating girls was a total failure. I wasn't out to any friends/family at this point, but I started seeing someone who was completely out (he was about 22). I looked up to him as a role model because I saw how little anyone actually cared about him being gay and this was the first sort of spark of confidence in the idea that coming out would be no problem. But being on a varsity team, I wasn't sure how coming out would change my relationships with a group of people that I spent 30+ hours per week with. It was a bit of a psychological tug-of-war, but I realized that it was not me pulling on one end and my relationships with my friends on the other; it was what my relationship with this could be if I was out vs the uncertainty about my friendships.
I think for a long-term meaningful relationship to grow and to legitimately become important to each other, you both have to be out to at least a few of your closest friends and some family. At some point, one/both of you will hit a wall where you want to go further (and all the chemistry is there), but you'll hit the wall of privacy that's protecting you from the scrutiny of others and going further without breaking that wall will be impossible. In short, if one or both of you isn't out, it is an almost certain limit on the potential of your relationship with them and if you agree to date someone who is in the closet, the only saving grace is the possibility of them coming out when you hit the wall or before then. Personally, the risk of getting that far and running out of gas when we don't have to isn't attractive enough to be kept a secret.