Im only 17, so i dont know all that much about relationships, but i could reccommend getting a couple of longboards and setting them aside for a day when its not too hot out, preferably with a nice breeze. No water needed except for drinking, and even then it dosent have to be water.
I mean, just imagine you're riding down say, a mountainside, you hold your hand out and let the breeze flow through your fingers. You look over and theres your boyfriend right beside you!
I dont know iff that would be something either of you would enjoy, but its a fun and relaxing way to spend time together, get out of the house, and maybe even stay in shape!
Hope this helps, and best of luck!