TS2 Sims learn by doing. You might have to encourage more social and romantic actions between this couple. There is a reason I didn't like FT and it wasn't just the easy peasy mood busters it added, such as slow comfort motives or slow bladder needs etc. It was it changed the original game in so many ways that I played without it for years until TS2UC.
As far as Sims kissing each other hello or goodbye, yes, it's a thing in TS2 and nothing you can do about it unless you install a mod to stop such stuff they do autonomously. They won't remember and it seems like it's some devs' joke. They added lots of little details some like and some don't. Pescado probably had a mod to mod this out, too, at More Awesome Than You website. You might could look there for a mod because other Sims will do that, too.
Once the Sim figures out (if they can) you would prefer they sing to each other, kiss each other or whatever, that will be all they will do for awhile until they get interested in something else. If their wants won't roll a different one taking them to a community helps jar that loose and make them roll something else.
Spring time in Seasons (another game changer) will make even a loner, Knowledge Sim want to flirt, go out to dinner, kiss or fall in love. Seaons and FT are game changers, they change what Sims think about. Family Sims (before FT) used to favor one child over another, the Ottomas family is a good example. No matter how many times I tried to break that mother from wanting to be friends with David, be besties etc. she kept wishing to play, talk, hug, etc. etc. with the oldest child couldn't have cared less about her other children. lol Now with FT installed all they do is behave like Popularity Sims always wanting more friends etc. Even my Knowledge Sims do that, but it's just not FT it's the BFF patch, where it changed or let's say interrupted the natural flow of a Sim's wishes so now it's either become a BFF or work toward that goal.
I lock up Sims who won't roll the right aspiration wants....in an asylum, without food, or water, or comfort until they do. They finally get it and wish for something else besides their obsession. It works. >:)
Some patches changed the natural flow too, and you might be find the original unpatched game is very different (the base) than the game today with all patches and EPs installed. They removed attractions to some objects, so they no longer will even roll a wish to use it anymore in some cases, they removed the threat of death to a very low number, (other than fire) and the later EPs will always override base game concepts. Don't get me wrong, I liked AL very much however, it changes Sims and the game is different without it installed, too.
