I'm designing a "adaptive" humans where repeated physical contact, skin on skin or exchange of bodily fluids, over prolonged period affects the development of the individuals.
The effect I want to achieve is that people who are in extensive physical contact for a quite a long time adapt their physical look and behavior, sort of like the funny pictures where old couples start to look like each other. The change is not very large but it's large enough to be noticeable.
For example imagine a couple that just started dating, where a man is a gym rat who only reads the sports section & woman loves foreign cultures and never lifted anything heavy in her life.
Within a few months man will start to feel strange affection in reading Nepal and woman would't understand how she survived her life so far without going to fitness club. If they broke up the effects will fade in few months, if they stay for a few years the effects will become permanent.
I'm not talking about pretending that you like something, they're starting to really like it.
I want to explain it with some mechanism that already exists in the animal world and could plausibly work on "humans". I know that human semen has antidepressant effect. Ants & Termites use pheromones but that seems far fetched for humans, since they live in colonies. Is there anything similar from our closer relatives where there are two fertile sexes, preferably mammals?