Having been in combat and losing friends, I know that dark place we sometimes find ourselves in.
This game does build a sense of brotherhood if you find the right group of guys.
Having been in a similar spot and thought process as you I offer you this...
...always know that there is at least someone out there that cares about you. Life will go on with or without you so don't consider taking yourself out. Life has much to offer, good or bad. Part of what makes us who we are is the people in our lives (past, present, and future). Honor your friends by moving on with your life. You can't "what if" things as they have already occurred. Learn from mistakes, whether yours or someone else's and become the best person you possibly can. You make your own destiny. Though I am not a religious person, I do believe He has a bigger plan for each of us and that things happen for a reason.
If you are ever down and need someone to talk to, please PM me and I'll give you my phone number. I am willing to talk if you need it!

SlipKnoT