I've fallen for my ex's best friend...help?

i dated this girl for 5 years and we were extremely close. things went down hill when she became a controlling psycho and wouldn't let me do anything without her supervision or permission. it got to the point where i was required to give her updates of every single thing that i was doing every second of the day. you can imagine where the love began to slowly diminish and everything became a chore. we broke up over a month ago but are trying to be civil and stay friends. being together for 5 years we had basically the same friends and now that we broke up I've been getting a lot closer to one in particular. we grew intimate and have very strong feelings for each other. not many people know of how we feel towards each other besides a select few and we want or at least hope of a future together, however one thing is stopping us. we keep thinking about my ex and how it would crush her to know that we were together. we've limited ourselves from each other because we want each other so badly but don't feel its morally right to continue. should we continue to be with each other and come out with it? should we keep it a secret until the dust has settled but risk her finding out from someone else? should we stop seeing each other and try to get over each other? we are both highly confused. help is greatly appreciated.