(1) is true, if utterered by me.
(1) christine is my former future roommate 
it's true because back in june, i had some concrete plans and a commitment to sharing a place with christine.
but since then, the plan fell apart, and i have no expectation that we will ever live together in the future. i would be lying if i uttered (2).
(2) christine is my future roommate
in general, (3) is false in the present and in all points past, if uttered by me.
(3) christine is (currently) my roommate
suppose 
former and 
future are operators that shift times, without any additional modality. then (1) can be represented as in (1'), or in terms of time operators 
past and 
future, as in (1'').
(1') former[future[christine is my roommate]]
(1'') past[future[christine is my roommate]]
if the time of the utterance is t1, then (1) would mean that there is are points in time t2 and t3, such that t2 precedes t1 and t3 follows t2, and 
christine is my (current) roommate is true (when uttered by me) at t3.
but given that (1) is true when uttered by me, and given that (3) has never been and will never be true, this analysis appears to be wrong.
why? i blame the word 
future, which appears to include an element of modality, specifically modality of prediction or expectation, not unlike the future modal 
will.
my problem with this analysis is, it doesn't seem to me that (4) is true when uttered, if it happens to be a plausibly surmised but factually wrong statement about the future.
(4) jane is my future wife
[notice, though, that if i will propose to jane tonight, it is true that she is my future future wife).
in any case, the facts above are not limited to the word 
future, but also apply to other (apparent) adjectives and nouns:
my soon-to-be roommate
the president-to-be
are all futures in natural language really modal?