Most people on here will tell you to be honest with her.

I don’t see the reason. If you were going to stay with her, she would definitely be entitled to all the details so she could make an informed decision.

If you are planning on breaking up with her anyway, I don’t see the need to throw an additional insult to injury. What benefit would this have? She would feel like shit. Develop trust issues for the next person who doesn’t deserve it. She would feel bad about herself when it was really YOU who fucked up.

People on Reddit love to shout “tell them! Tell them!” But I really think it’s best to look at who would actually benefit from this. Maybe you’d feel better by easing your conscious. But she would feel like absolute shit.

Just my 2 cents. Break up. Tell her things aren’t working out. Don’t get back with her. Ever.

Edit to add: I missed the part where it was her friend. This changes everything. OP, you need to tell her. She will find out one way or another