RECURRENT STRABISUM. Eye be effected?

I was treated for exotropia at the age of 6 successfully but it has occurred again in the same eye. ( WHY SUCH THINGS HAPPENS) Presently my vision is 6/9 with this eye. Now my age is 25. What should I do now? Squint angle is 15°, and Doctor said that they have to operate on the other eye to straighten this affected eye because the affected eye was already treated at 6 years of age, How do they handle this by operating on the healthy eye! I am afraid if this will create a problem in the healthy eye too. What if I don't go for surgery ? Will my vision in the squinted eye be effected? As I am seeing quite good as compared to my healthy eye right now. Visual acuity 6/6 and 6/9 ( squinted eye). This squint has been there again for 4 years but my visual acuity in the affected eye hasn't changed since . Is it good idea to get operated for the squint again, that too in the healthy eye! Please help.