Missing someone is your heart's way of reminding you that you love them. Instead of being sad choose to think about the good memories and all the joy you shared. This does make me think of my wonderful Mom. I miss you soooooooo much.
Try not to stress over the shady people who betrayed you. I know it hurts, but the truth is that they were always shady, they're never going to change, and you're actually much better off now because at least you know who they really are. (For my friend)