The problem is the perspective with which you have chosen to view interactions. While you view interactions as either one-sided or mutually beneficial usage of two people not everyone interprets these actions the same way. And while you may believe to understand the intentions of one person some of us are odd, and we approach various situations in strange ways which may give off the wrong signals.

I only say this because I agree with you, in regards to the fact that even the "best of friends" are only friends because they have found use in each other in ways such as common interests or necessity. The problem is despite the fact our viewpoints may be valid they are uncommon and inhibit interactions with others.

Despite my best attempts to earn friendships I often find myself sacrificing too much of my time or my money in order to help the other person while little reciprocation takes place. This in turn makes me feel dejected and pushes me further into isolation.

So despite what it is, you have to ask yourself "can I change my perspective?". Otherwise you will likely never find comfort in the company of others.

If I missed the mark I apologize for any poor advice or understanding on my behalf.