Fun Places for Couples in Colombo

I am going to Sri Lanka for the first time without my parents (I am Sri Lankan, obviously, haha) and taking my fiancee with me (he isn't Sri Lankan).

Usually, when I am in Sri Lanka, I see family and visit temples. However, since I am with my fiancee, I wanted to see if there were things I should do with him in Colombo while I am there. TIA!