Actually, Chive, I've just always tried to be sensitive to *other* people's feelings, sometimes to a fault. What usually happens is, I'll make a new friend, I'll treat my friend well, and vice versa, until something makes it inconvenient for said friend to reciprocate in kind (a significant other, a sorority, new, cooler friends who drink, or just being "too busy" to honour commitments that they made to me), and I'll let it go for the first few times, but then, at some point, I finally snap and (politely) say that this kind of treatment just won't fly, and at that point, my friend drops me. You'd think I'd know better by now, and I know *rationally,* but I've never been able to act on it.
I wonder if you're rushing it, or assuming that these other people want friendships, when they really want acquaintance-ships? I'm not saying this to criticize but to give you another perspective. It sounds terrible, but I have all the FRIEND friends I really need in my life. Now, if I've known someone as an acquaintance, for a pretty long time, it sometimes, pretty rarely, moves on over time to a true friend level- the kind of person I feel I need to be "there" for when they need something, and expect to be there for me. But you need to know the other person for a pretty long time in my experience before you have a good feel for if this is something you want, AND something they want- then there's the whole issue of if you really click on that level. I'm not unfriendly and have lots of acquaintances, people I've gone to school with, worked with, and got along famously with, but then circumstances change and we move on.
I'm much much older than you, and this has worked for me pretty well. Don't make the mistake of thinking everyone you're friendly with has to be your really close friend. Some people just aren't up for the job for whatever reason, and you'll grow apart in time anyway. Work on being a good casual friend and don't worry about how long it lasts or how deep the friendship is. You're obviously a very fun and thoughtful person. Over time, the right ones will develop into true friendships so you'll have that. In the meantime you can enjoy hanging out with people you are simply friendly with, and who will disappear as your circumstances change.
Sorry, got in a preachy mode there for a minute. But this seems to hurt you and I hate to see that. Quality is way more important than quantity in friendships. I'd rather have one person who I wouldn't hesitate to ask a huge imposting favor of, then 100 people who would be ready to go to the movies with me at the drop of a hat. And to be a real true friend is a lot of work because you HAVE to be there for each other no matter what. If people are telling you they aren't ready for that with you, it's not necessarily a reflection on you. We have a limited amount of time and emotional energy, and need to save it for the things that are truly important to us.
Sorry for the lecture- eek. Don't know what got into me.