Need help opening up

My depression has its roots in childhood bullying which left me feeling like I had to be on guard all the time. I figured if I hide any weakness and keep all emotions to myself it gave my bullies less ammunition. That mindset became a way of life and now I bottle up all emotions for nobody to see. I know I would benefit from talking to someone but I can't bring myself to talk to anyone about what I'm going through... even my fiance. I'm filled with fears, grief, sadness, and a trust issue that keeps me from opening up to anyone. How can I start to let my guard down so I can start on a better path?