Is my uncle's wife complicit with me in our actions.....?

No she's not,,,you both share equally,,,,No don't tell your uncle(he may not believe you and it may cause a biiiiiiiiig problem, most likely bringing a host of other family members into it),,,,You may not have been the only guy she's done on the side,,(women like her that will do another member of the spouse's family, is not worth destroying your relationship with your family),,,,,,It is time for you to pack your bags-----no more visits,,,,from this point on it should be phone calls to uncle only,,,,,,,,,,