orlando - disney world, seaworld, discovery cove (swim with dolphins), universal studios, etc.
florida in general - lots of beaches and nice weather
california - southern california is the same as florida except you have the pacific ocean
US territories:
US virgin islands - no passport required for US citizens. there are 3 main ones: st. thomas, st. john, and st. croix. there are direct flights to st. thomas available from east coast airports. you usually need a ferry to get to the others from there, but st. thomas is gorgeous itself. beautiful beaches, watersports, and you can definitely just relax together.
puerto rico - also no passport required. beaches, watersports again. they have the rainforest and the bacardi rum distillery, which may be more for you since you guys are definitely of age to drink ha.
hawaii - famous beaches, different culture to be experienced.
i would personally pick disney or one of the islands. i would go scuba diving, hang out at the beach, and get a massage with my loved one. have a good trip!