Sometimes I feel that it can be a lucrative trap to become invested in a single person, and then accumulate expectations that far outweigh the responsible obligations of any friendship.
As I have gotten older, a pattern that is working much better for me is the campfire model - I just try to keep a metaphorical campfire going, for people traveling through this life to stop and warm themselves upon while I tend it. I cannot know which direction people are traveling from, or to, or how long their journey has been or will be. But all people need to warm their calloused hands and feet, and I can keep this fire with a bed of rosy coals.
Sometimes someone will stop at my fire and warm themselves without my ever having paid attention, but to them it may have meant all the difference in the world. By keeping this obligation in mind, to simply expect people to need a place to sit a spell, I can at least believe I am helping.
The campfire is a nice way for me to remember we're all suffering, that not a one of us is unique to loneliness. Because sometimes that person who sits down at your fire is the person you have been waiting for, and only by making a seat for them were you able to ever meet.
Someone somewhere days, months, or years from now, needs your energy.