Is distance a valid reason to not marry a potential spouse, such as when the wife would be away from her husband for a few years for studies soon after the marriage?
In my opinion, yes, I do think it would be a valid reason to reject a marriage proposal. Ultimately, what we aspire to achieve in marriage is living together and forming a family.
Circumstances could arise during a marriage where a spouse must be away for a period of time, in which case consent from both sides is necessary. But if stay away from each other for long periods of time can be avoided, then that would be the best and healthiest thing to do.
If it is unavoidable, and will be for years, and they cannot travel together, nor see each other, then a decision must be made that would be equally fair for both. Getting married and then immediately leaving your wife/husband for a few years is not an ideal situation to be in, and if it can be avoided, then that is best for both.
With prayers for your success.