Well, I'm sure Kamikazi will be along soon to give the best answer, but let me at least give you some historical perspective in the meantime...
Plebe year, your roommates are assigned. You will most likely have zero choice. It comes with having zippo on your shoulderboards.
In my day, you had SOME leeway during your 3/C, 2/C, and 1/C years, but even then, the roomies were all from the same company. The higher you went in classes (3/C, 2/C, etc.) the more leeway you had, but you were still restricted to within company. Rooms were doled out by rank and lottery.
At that time, there was no provision made for rooming members of sports teams together. I wouldn't count on that being any different now.
Concerning who you keep for 4 years, I am uncertain what the "scramble" policy is these days, but in my day you could conceivably have the same roommate for as many as three years, and in VERY rare circumstances (dictated entirely by blind luck), you COULD conceivably end up going for 4, but that was almost entirely unheard of. The odds were simply too high against it.
My roommate and I (we are still friends, BTW), were roomies for 2.5 years.