I wasn't cheated on, but I went through a similar period of anger and suicidal depression when I was dumped from a 6 1/2 year relationship. Turns out it was the best thing that happened to me because my ex was controlling, emotionally abusive, and manipulative. I wouldn't have gotten myself out of it, so friends convinced him. What happened after that was me fighting my way through abject misery for several months.

What helped me was LOTS of reading, first. I spent a lot of time reading through all of Terry Pratchett's "Discworld" series. After that, I just started letting the anger at my ex come through more than the depression. The anger kept me going, and it kept me driven to succeed where he told me I would fail. I started regaining parts of myself that he'd crushed.

I know how bad the bad can be. Spend time with good friends. Flirt like crazy, have a few one-night stands. Do whatever you want that maybe you couldn't have while she was around. Smoke some weed, if you're so inclined. Throw yourself into a new project. Work really hard on something you've been putting off. Learn from this experience and come back stronger. You'll come to something better, and you might just meet someone better.