"Don't these people end up lonely?"
No Bohn, they don't EVER end up lonely. They always have a new rescuer lined up to move on to.
But the women who throw away their lives/children/sanity/careers/money/health/looks for them sure as hell do.
You don't have time to be worrying about his mental health dear girl, you need to be questioning your OWN.
(Said with much love & empathy & as the result of personal experience)