Why was i sad and miserable?

I have to get this off of my chest. I was really sad last Friday which was the reason for my crying and breaking down, when i should've been my strongest self. I have to give you a little back story before i get into this whole mess. I had this crush on a boy for about a year and a half until i got "together" with John. After him i didn't really have anyone i was crushing over, but i had boys who i liked to hang out with, so nothing serious. I am just not going to be together with someone who i truly don't like. It is just not me. So September comes around and i have to go back to school. I didn't think anything of it, i just knew that it is going to be really not pleasant and awkward between John and I. Which it totally was and still is. So i go in, and you know how every boy looks good in a suit? Well, if one of them is your ex/present crush, it is kind of hard to keep your eyes off. But i new that he had a girlfriend, so i didn't let me remember these feelings, i just ignored them. One day i had this idea to stalk his Twitter and i saw these really depressing RT, and i noticed that he only retweets stuff that he feels, not just random things. Every tweet was heading to his girlfriend cheating on him and all around that topic. So i come to the conclusion that he is single, hurting and that his now ex-girlfriend had cheated on him. Which, btw, not he not anyone EVER deserved to go through. So throughout September and October i kind of strt to have this feeling that i might interest him a little bit - all the little things that were adding up were too much to get ignored. So i started hoping, because i wanted to. Just because nothing worked out a year before, that doesn't mean there is no change of it working out a year later. So one day my friends and i talk about going to the cinema, we talk about everything - when, how much, who is coming, what film - while he is in the class. I knew that he was listening, but i didn't think anything of it. The night came and my friend and I went to the cinema an hour earlier, because we wanted to play games and be the first ones to buy the ticket, so we really choose where to sit. We played games and the hour passed ( we also had a funny/shameful moment, but that is not go anywhere near the story). We go to our seats and we are laughing, but in the back of my head i am hoping that he'll show up. I tun around and it is him...with a girl. Now, i know that it is not his ex, because i know how she looks like and this situation also proved that i was right about the break up in the first place. The weird part is that there are a lot of unpleasant rumors and not a good vibe about the girl all around town, so i don't understand why he was with her. I automatically am sad and i start to think about - whether they are together or not, whether they are just friends and ect. I am so sad. I didn't even have the strength to finish my popcorn, but i pushed myself to enjoy the movie at least. After the movie had ended i said goodbye to my friend and i went home. He had driven with his car, but i was walking. I was so sad. I didn't eventually understand what i was sad about -the situation, the boy, or the fact that he came with her. I started crying. Now i understand what it was. I wasn't crying for the boy, but the fact that i let myself get burned again, i know it is just a crush, but the little things he'd do just made me thing otherwise. I let myself get sucked into this trail again and leave the place crying. But i am not sad about the fact that i hoped. Never. I still hope, but at least i know what to expect if nothing goes my way.