welcome and sorry to hear about what you went through. i am not surprised at what you experienced. i have heard it happen before a few times i have been around. i do know that it is alot easier to not get in trouble if a sister does see more than one person. if a brother does it, much worse. why? not sure but it does seem that way.
where i am surprised is that you dated for three years. where i am at, from beginning to end in the courtship/dating process is frowned upon if you go past one year, two years maximum.