Everyone knows that parting is a very unpleasant business, which is fraught with a dramatic turn. On the other hand, if you know how to do it correctly, you can part gracefully and leave the "battlefield" without hysterical scenes.
Choose a suitable location
Try to choose a place where she can deal with unpleasant information. If you choose a restaurant, it will be a blow from your side, because, for example, if she starts crying, she will be subject to humiliating gazes from neighboring tables. Also, it is not entirely appropriate to tell her about your decision in the place where your first date happened, or has an equally sentimental meaning for her. At least don't spoil her memories.
Choose the right time
Holidays, birthdays, anniversaries and other similar events are not the best opportunity to inform her that she will never see you again. Indeed, is it necessary for her to associate Christmas once and for all with parting.
Do it in person
You may want to avoid an unpleasant confrontation and break up by phone or mail. Have the courage and tell her personally. This is about the minimum amount of decency and respect that you can show her.
Be honest but sensitive. If she starts asking questions, answer them honestly. Be sure that she will definitely find out about the reason for the breakup, and will hate you even more, because you lied to her. On the other hand, you do not need to explain to her that you are breaking off relations with her because she is a completely incompetent "board" in bed, and your new hobby is just a hurricane.