the 'colleague' story again. by end of the day ,no good ending for either u,ur colleague or ur ex gf.
probably u will know why later on if u try it out with ur colleague. u can leave ur gf of 3 years for someone else and of coz u will get it later on too.
it is just a cycle.

U did the right thing too by breaking up with ur ex coz u and ur ex gf can never be together again.
things wont be the same anymore and it was u who started it first.