Been there... not suicidal but faced with not running at all.. it sucks it sucks bad. I've been known as "the runner" since Jr High and now poof it's gone. It really does feel like your identity is gone and that your purpose is gone.. so you are "gone."
While it seems minor to everyone else ( "hey just try swimming!!") for you it is your entire world. I do think you need to talk to a coach or counselor. I'd recommend a coach or ex athlete over generic counselor because they just won't "get it."
Losing your sport is tough. Look at how bad former athletes fair once they are no longer playing. It's why so many immediately get right back into some are of the sport once they are no longer a competitive athlete. It's because they cannot imagine their life without it.
Good luck and seek help!