A guy I went out with for about 7 months was in the same class as Stipe at UGA back in '78-'82.
After we broke up, we were having lunch and he shared with me that he had lived with MS for a year while in school. They (the guys in REM) had taken over an old abandoned church in Athens, and it served as a combination living space/practice hall. Todd had never discussed the issue of his bi-sexuality with me while we were together, but I have to admit, I was anything but shocked by the revelation. He was 6'4, looked EXACTLY like Rock Hudson circa "Giant" days and had an incredible sense of self deprecating humor mixed with more sensitivity than most men I'd known. He went on to marry and father 3 boys, but I wonder if his other side popped up from time to time.
And no, I don't know whether MS is a top or a bottom. For all I know, and this isn't delusional thinking, they may have just been into mutual sucking and other non penetrating sex.