Meursault doesn't care about anything so therefore he can't connect to anything. His friends and Marie are just possessions to him, he uses them to keep himself busy or to entertain himself. I would argue that someone who is truly connected to someone doesn't "use" that person, they respect that person and care about how they feel and feel real concern for them. This connection could be called friendship or love, but those are just varying degrees of the same feeling. Connection also implies empathy, for people to be connected they have to understand each other's feelings. When we talked about Banach's lectures I came to the conclusion that people can share common experiences, emotions are part of that experience and are an experience that most people connect to.
Meurasult is different, he doesn't feel emotions (at least not until the end of the book in which case he doesn't express them) so he can't connect to someone's feelings. He couldn't connect to the woman at the funeral who was crying, or his friends or Marie. As we've seen throughout "The Stranger", not being connected leads to hollow meaningless relationships. By association we have to feel emotions to connect to people to have meaningful relationships to add meaning to our lives.