Welcome to the community. That sure is a slow growing cyst! If they get too large, you run the risk of ovarian torsion which can be very painful as well as running the risk of losing the ovary (since it chokes off the blood supply). It seems I have read the "cut off" for monitoring a cyst is 7cm but then I have heard of women having larger cysts that did not cause torsion (I had a 9.5cm complex cyst). That being said, since this cyst has not resolved in 3 years, it likely never will. It is best to have just the cyst removed (cystectomy) since the ovaries have LIFELONG functions of producing various hormones up to at least age 80 for optimal health and well-being. Removal of even one ovary can permanently disrupt ovarian hormone production as the "system" is circumvented. The other ovary may "pick up the slack" but there is no guarantee this will happen. Unfortunately, many women lose an ovary(ies) for ovarian cysts when that is unnecessary.
Best of luck to you in getting proper treatment.