The Antalya coast offers very different kinds of romance within a few hours of one airport: a historic walled old town, long sandy beaches with big resorts, pine-covered bays below the mountains and small harbour towns on the Lycian coast. You can mix a few lazy resort days with sunsets, boat trips and ancient ruins without long internal flights.
The most important decision is the style of your trip: lively and cultural, quiet and scenic, or all-inclusive comfort. The areas below match those three moods. Many couples also split the trip, for example a few nights in Kaleiçi followed by a week at a beach resort, which is easy to arrange with one private car between the two hotels.