Repenting for Deviant Sex Precept
Yes it is a violation of the Deviant Sex Precept if you have already received the Five Precepts.
It is very difficult to repent but it can be done. I am not at liberty to discuss it publicly; otherwise I would be breaking Precepts myself. Also, you cannot “retake” the Deviant Sex Precept until after your offenses have been erased.
Generally speaking, I hope that left-home people would properly train their disciples on the Precepts, their meaning and responsibilities, before transmitting the Precepts to them. I was also not trained when I received them from my Chinese teacher and simply “lucked-out,” because somehow, I avoided committing violations before I thoroughly understood the responsibilities of receiving them. Perhaps if you would also ask these questions of the left-home people at your temple, they will come to realize that they need further training to help you.