There should be a "romance multiple people" option that could open up with sufficient charm/intimidate (I would've just said charm, but maybe the characters like being ordered around by you and thus intimidate could be of use instead?). That way you can take the third option instead of breaking up with one person or the other(s).
It could be Bioware pushing the envelope. ME1 had FF romance. ME2 could have threesomes! ME3 could thus have orgies! ... but that'd probably push the envelope out of M territory, no matter how much it's not shown. :?
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gman, don't forget the "missing the jokes" portions.
Kaiden's my cannon fodder. The only time I might let him survive is to get the achievement for using him most of the game. If you use him all the time up to that decision and you let him die there, do you still get the achievement?