Any party can be guilty of staying only for as long as their fleeting needs are being met (the way many men will leave women after many years for someone younger), but in all of those cases, why would you want someone to stay around who doesn't want to be there? If she's there for "security," it doesn't mean she likes you; it means she's being taken care of. And if she doesn't like you, she can still find someone else she does like while you fulfill that "need" for security.

If that's fine with you, no judgment. But someone needing you doesn't guarantee that they actually WANT to be there. They may feel like they have no other choice.