My pet theory on the Garak/Bashir/O’Brien triangle is that Julian was involved with Garak following that juicy pick-up scene in “Past Prologue,” and then switched to Miles at the end of the third season. I blame Garak’s torturing Odo in “The Die Is Cast” for this–obviously Julian couldn’t take it.
The transition between the two relationships is abrupt. In “Improbable Cause,” Julian and Garak are exchanging gift chocolates; two episodes later, there’s Miles and Julian drunk off their asses, singing “Jerusalem,” and Miles just about telling Julian he loves him.
I got a lot of fanfic mileage out of that. 