Santiago met Bowen Unger when out one time:

Short story short - he moved in cause he seemed an okay sim:
 Hi traits are as follows: loner, genious, mean (uh-oh), gregarious and his aspiration is friend of the world. And he works as a tech guru, earning more than Santiago.

One night, this happened again:
She was alright though.

This also happened:

The pair became a couple

The couple worked out together

Bowen struggled to lose weight

Santiago on the other hand started to look nicer

So the time came to focus on the new heir, so the girls, Diana and Getter, had to move out, in with the rest of the Goldsmith family outcats.

The last days at the house for the girls...

Could've been

Is