Sounds like a "based on a true story" book. Don't try to pull it off as a piece of non-fiction if you don't have all the facts (James Frey tried that and ended up in hot water). You can write it as fiction that is based on a true story and that gets you out of any trouble filling in the spaces.
Two things:
1. If you're using your real name on the jacket cover and the events are very close to what happened, you should accept the consequences if the subjects of the book find out. If it is published, there are still slim chances they will pick it up (unless they google your name), but don't write it if it would be truly damaging to their lives or otherwise unacceptable to you if they found out.
2. Be your own hardest critique on this: most people who want to write about their own lives or something that happened to them think that it is far more interesting than anyone else does. The experience may be genuinely interesting: you may have witnessed a murder in your sleepy little town, or one of your colleagues may have embezzled ten million dollars from one of the failed banks (in both cases you should go to the police, not write a book); or you may be such a gifted writer that you can make a fairly mundane, life's-little-moments story come alive like Hemingway or Gabriel Garcia Marquez.
But if you want to write about ex-wives or ex-friends or ex-colleagues and the crazy stuff you used to do - ask a few people (who aren't current friends) and see if anyone else finds it as interesting as you do.
Good luck!
