Oooh!
Charlotte - Trey and Harry
Samantha - Richard and Smith
Miranda - Steve and Robert and Steve again
Carrie - Big, Aiden, Aiden again, Berger (well, I don't think she ever loved him, but I guess he counts as a major relationship), Alexsandr, and of course, Big again.
Samantha was the one who briefly had a lesbian relationship - I think her name was Maria...