When we interact with people, we do so in many different ways. Some are very passive such as when we are ordering a coffee. Some are very involved, like when you would go on a date. Based on how much or how little we interact with someone, the content of those interactions, the outcome, and the perceived vibe determines how we categorize our relationship to the other person. If you were to hang out with someone almost everyday, you would probably say they were one of your best friends or at least a good friends. If you were to hang out or talk with someone only once a week or less, you would say they were more just an acquaintance. These are pretty loose guidelines of how one would sort people in their minds, but what happens when one is left in mystery?
When you first meet someone you usually try and put your best foot forward. You show the best and most unique parts of yourself. The parts that separate you from everyone else. This attitude most likely will be reciprocated upon you. You experience the best parts of the other person. It is at this point where you decide in your mind whether or not you would like to talk with them again, or if it was merely a one off deal. You begin to form a friendship when you both found that you enjoyed the other one's company.
I am not merely referring to finding a boyfriend/girlfriend, but to any form of friend. If you can't stand the other person you will make no effort to talk with them, and will even take steps to make sure that any interactions you have with them are few, short, and far between. That holds true to any kind of relationship, platonic or otherwise. If you value the other person, or care about them, you will try to make at least some effort to talk with them. I know in school there are many things that can divert out attention, but when you value someone you will make time for them. Just like working out, studying, and eating, if you think it to be important you will invest time into it.
So you and this other person have already decided that you enjoy each other to some degree, or at least that is what one thinks. A few days later one initiates a conversation with the other. You had a great time and are trying to make, what you think is the beginning of a friendship, into a more solid one. You start talking with them and everything seems to be going fine. They actually messaged back/answered the phone, and you think everything is how it should be going.
But one day something seems to be off. You have noticed that you have been the only one initiating conversations. That the conversations seem to be very plain, very off setting, almost like you are talking with yourself. What happened, you ask yourself. You thought things were fine, and nothing has been explicitly said contrary to that. But you can tell when things seem off. Whenever you see them they give you a quick smile and ask how you are doing, but they have no intention of delving deeper. You are only receiving common pleasantries.
At this point, you have received the message. You have built a delusion about the nature of your relationship with the other person. It all began when you first talked with them, and only manifested itself further the longer you tried talking with them. You thought wrong. The other person had no intention of becoming your friend. They were just being nice. You read into what they said and did. You put yourself out there and you were discounted. Yes, you did not make a friend, you ran right into a dead end. You put your best self out there and they have handed out their judgement.