This one is very sneaky indeed. Unlike the previously explained point (the one where they like to spend time outside without you and are very secretive about the things they do when they are not with you), they encourage you to spend more time with your friends and family. Under that pretense, they go out and have all the time to spend it however they want. This sign is particularly disingenuous because they want to look like they are the good guys in the relationship.
This trick can be pretty hard to spot, as at first, you might feel as if your partner has good intentions. Yet, as time goes on, you will start noticing the pattern, where they are trying to get you to get out of the house so that they can continue with their "business." The only way to stop this is to be open and summon them about their behavior.