I do feel useless if I don't do something with/for someone I care about. A lover I have deep feelings for and who reciprocates those feelings is better, but friends have the same effect, although it's less intense.
I guess it depends on how dependent your personality is, and how much self-esteem you have. Someone with a dependent personality has a strong desire to feel the security of depending of someone. Someone with low self-esteem might have a similar behaviour, too. Either because they're insecure and seek the approval of someone, either because they want to feel in control of that person to boost their ego. And of course, the need for affection, which varies a lot.
I'm like that, personally, in three ways. Everything in my life is okay when I can rely on someone. Alone I'm a mess. The only part of my life when I was really happy and hopeful for the future was when I had a girlfriend. I feel an overwhelming desire to have someone I need, and someone who needs me.
Just one last thing. From the group therapy I was at, I learned about the feeling of "internal emptiness". To feel empty inside. They asked people if/how much they felt it, and since I didn't understand what it meant at all, I asked. They said it's normal not to understand; that people who have that feeling understand and know it. Apparently, this is a psychological symptom that's really bad. I completely forgot even the biggest details, but if you really feel empty inside, I think it would be wise to consult.
