Theres this girl, I've known for about 2 years now...?

Theres this girl, I've known for about 2 years now. She's also my neighbor. We met because I was friends with one of her friends and we kind of got introduced. That day I was walking home, I met her on the way and found out that she lives across the street from me. As soon as we met I was instantly attracted to her, she just looked so beautiful in the sunlight and everything. After that she would invite me over to her house and stuff to play Halo or something and a lot of "ackward" moments would occur. Like she would purposely sit on my lap, and me not being used to reacting to ackward situations like that, I would just like stare in shock. I didn't know what to do. Another day she said she wanted someone to talk to at night so I went over and we were sitting in "her" car. It wasn't even a legit conversation because the weather was so cold and I couldn't stop shivering. She put her hand on my face and I didn't know what to do. I got used to her and started to love her kind of. Like some sort of sister but way more than that. I would give her casual presents from time to time like chocolate and stuff and she loved it. My mom kind of started wondering where I was sometimes at night so she stole my phone and checked my texts and flipped out when she found a text saying to meet somewhere with this girl. My mom, being the b*tch that she is, proceeded to call the girl's cell very early in the morning; the girl's mom, being a nice lady, picked up the phone and tried to calm my mom, who was thinking that the girl is just a whore after me for idkwtf my mom was thinking. The girl's mom kept telling my mom that her daughter feels safer with me and everything and all that. I still never got it, but now I understand. This girl has had 2 other relationships after that incident and they all failed horribly. We still talked a lot after our mothers had that little brawl, but I never see her laugh like she did when we first met and she wouldn't really accept any presents I give to her, not even for christmas. Its like something died. When I realized that I neglected her like that and its me that screwed up everthing cried and got really depressed, grades started to drop etc. I kind of got slightly over it but i can never get her beautiful face out of my head. I would always think, at least i can stilil see her at school and talk to her. But, now to make it worse she's in another "bound to fail" relationship and my parents told me that we were going to be moving within the next few months. I DON'T KNOW WHAT TO DO, I STILL LOVE HER SO MUCH BUT I CANT DO ANYTHING BECAUSE SHES ALREADY IN A RELATIONSHIP AND I MIGHT NEVER GET TO SEE HER AGAIN!!! HELP WHAT SHOULD I DO I'M REALLY SCARED I WONT GET TO SEE HER AGAIN