There are other ways of establishing their relationship, or make people interested in the characters. Maybe you can have them do stuff together for a while before him looking for her. It's more important for the player to like the character and want to help a certain character, not that the character they are playing as finds the person important. Heck, for the Persona games, when it came to the party social links, people more likely did it because they were invested in the character already (along with the perks).
I feel that sex being used so haphazardly is not a good thing. Yes, it can show a close relationship, but with how it's been used in media, especially video games, it seems more like pleasure and gratification than anything emotional. Showing is more than telling, but if you just show sex, that's not really doing much. While not the greatest, Shadow of Mordor did an overall good job of showing the relationship of the guy and his family.
I feel that sex being used so haphazardly is not a good thing. Yes, it can show a close relationship, but with how it's been used in media, especially video games, it seems more like pleasure and gratification than anything emotional. Showing is more than telling, but if you just show sex, that's not really doing much. While not the greatest, Shadow of Mordor did an overall good job of showing the relationship of the guy and his family.