Sayid dated Shannon. Slept together in a tent.

Kate slept with Sawyer three times. Once by climbing out of her cage through a gap on roof and entering in Sawyer's cage by breaking the padlock. Later she jumped on Sawyer after watching Jack with Juliet. The third time was in Sawyer's house where the Others live. They've kissed a few more times.
One in the tent after sleeping when Kate goes back to her tent.
One when they were working on the runway.

Ana Lucia jumped on Sawyer to take the gun. When that didn't work she made love with him, then stole the gun.

Jack kissed Juliet.

Juliet slept with Goodwin.

Goodwin was married to the therapist.

Hurley liked Libby, and she kissed him, twice.

Rose & Bernard are married. Kissed.

Sun & Jin are married, had sex on the island but we've never seen it. We know because she's pregnant. And many kisses.

Paulo & Nikki were dating. Had sex in a deleted scene.

Alex & Carl were dating and kissed a few times on screen.

Danny & Colleen were married.

Claire & Charlie had a little thing going on. Kissed we're pretty sure twice. They obviously had feelings.

Jack confessed his love with Kate, so did Sawyer.

Smoke Monster cuddled with Locke.

Boone was in love with his . . . stepsister Shannon.

Juliet and Sawyer now a couple. He said he loved her