FemShep-
In ME1, setup a 3some with Kaiden and Liara, Kaiden wussed out, so Liara.
In ME2, Garrus, but boinked Liara after the events of the Shadow Broker. I boinked Garrus after SB mission, he seemed cool with my polyamory.
In ME3, Garrus. Maybe I should have tried to 3some a Garrus-Liara setup? Can you do that?
For BoyShep-
In ME1, Liara. I found Ashley racist, so she dead, brah.
In ME2, Jack. Was very tempted by Tali, but I think Jack more damaged. I wanted to show her there was such a thing as love that didn't end in betrayal. I boinked Liara after the events of the Shadow Broker. I boinked Jack after SB mission, she seemed cool with my polyamory.
In ME3, well, I've only just started playing my BoyShep in ME3. Maybe Tali?