Hey there
I totally get what you're saying about feeling like you won't be good enough for another person, feeling like you shouldn't even bother trying. I feel that way quite a lot, and the way I see it is that there isn't much you can do about it... we're teens, it's pretty much inevitable that we're craving for a relationship, and for many of us we'll be too anxious thinking about it to have time to actually do anything about it.
I think the best ways to go about this whole issue are 1- stop analyzing conversations, and put aside any thoughts of you not being "good enough" for a particular person; 2- when socializing with people to whom you are attracted, try to stop thinking of them as a "potential partner", and instead, try to develop your relationship slowly without that goal in mind; 3- don't take it too seriously. You win some, you lose some, and you can't do anything about it. You can't make someone like you.
Hope this helps a little
Skye