Funny how the closest people can become complete strangers in the spam of a very short time. It hurts, it does. You try to let someone go but it isn't as easy said as it's done. But then I think, if that person isn't willing to stay by my side then there must be a good reason for that. Maybe they weren't for you in the first place? You never know what they said about you behind their back nor their actual feelings, if it was fake or not. If you're missing someone who stopped talking to you or let you down, let them miss you, not the opposite. It's their loss, not yours. You'll always be better, more mature, and most importantly kinder than that person. I've learnt not to get too emotionally attached to someone if I'm not too certain about that person. Sure, trust issues accompany that, and that has its disadvantages.
Giving your trust to someone or leaning on them surely isn't easy, and will really hurt when that person backstabs you, but remember you'll get through this. If you need to anyone to talk to, I'm here :)