I am truly sorry to read about the pain I know you are going through. I have been there myself and know how helpless, lost, and hopeless you feel right now. I will give you my advice, but I must warn you that advice is only as good as you make it.
First, the thoughts of suicide at this point are normal, but you have to stop! I hear your response, it's easier to say than to do, but it is actually that easy! When they come, you stop them! You think about something else. You cast them out of your mind. Your going to look back on this someday, just as I have, and realize how ridiculous those thoughts actually were, and be thankful you didn't act on them.
Second, let the guy go! I'm not saying you won't someday be back together, but if that is even remotely possible, you're going to have to let him go now. Hanging on will only push the person farther away and will also make you look ridiculous. You are not ridiculous! You are lonely, stressed, lost, and in shock, but you are not ridiculous. Do not let him or anyone else make you feel that way. You have to let go now! No phone calls, emails, letters, nothing!
Third, get on with your life as you want it to be. Don't go looking for a new partner, and as I said in point 2, don't look to take the old one back. Find yourself. Find the person you want to be. By that I mean, are there anythings about yourself you wish were different? Now is the time to fix them. Fix you! When your in a relationship you have little to no time for you. See this in a positive light and take the time to correct mistakes or missed opportunities. Too fat? Lose the weight you've been meaning to lose. Feel stupid? Go back to school or start taking those classes you've been meaning to take. Watch too much t.V.? Stop! Get a hobby, do something fun. Find out who you are!
By the way, it probably sounds like this is coming from a female point of view? It's not. I am a 42 year old male who went through the same thing. I got married in 1981, cheated on my wife in 1982, we worked through it, had 2 kids, she decided she wanted more in 2000. Left me with the 2 teens, mortgage, car payments etc. After 20 years of marriage. Everything I told you to do is the things I should have done and eventually did after 2 years of putting myself through hell. Don't wait! You can fix yourself on your own. You do not need him. You'll thank me later if you'll just listen.