That's a tough question. I was single when I went through gradschool and in a way it was a good thing, 'cause I could be somewhat myopic about my schedule. If I needed to stay up late studying or go to the library all day Saturday, I could do that without worrying about neglecting my spouse.

(Fast forward some years.)

On the other hand, my wife went through gradschool and had my financial and emotional support. I didn't get to see her as much as I would have liked to, but our marriage is a longterm deal, while the inconvenience of gradschool was just a "season."

I suppose I would encourage you to not get married until after gradschool, if for no other reason than you will be a little bit older than you are currently. I know that you are convinced that you've found your soulmate (and maybe you have), but statistics are not good for getting married at 20 or 21. The things you will learn about yourself in the next few years could be more significant than what you learned in the last few years. And if you guys are right for each other, waiting a little bit won't hurt you at all since you're considering a longterm committment anyway, right?