bill and coo (old-fashioned)
If you bill and coo with someone you love, you talk quietly to them and kiss them.
EX: [/i]I don't know why they bother to come out if they're going to spend all their time billing and cooing.[/i] (often in continuous tenses)
Note, 'bill' refers to a bird's beak, and 'coo' is the sound a bird makes when it is content.