I have never let things like oh my friend dated this guy hold me back nor should you....you get one spin around the sun...it didn't work out it didn't work out...why be held back?
You're both single, I assume. You can date whomever you choose. It MAY hurt your ex, but your ex should be adult enough to allow you to both live your lives whether you date one another, or not. The ex should also be able to move on as well. Life isn't easy. Love and heartbreak certainly are not easy, but it's all part of it. Every choice doesn't and shouldn't make EVERYONE happy all the time. You've both waited a very long time to even share your feelings for one another. If you really do care for each other, go out.