Maxine McGill found Alice Ruggles, 24, with her throat cut from ear to ear at the Gateshead flat they shared in October.
Serving soldier Trimaan "Harry" Dhillon, 26, was jailed for a minimum of 22 years for Miss Ruggles' murder.
Ms McGill said she would "never feel the same again".
The trial at Newcastle Crown Court last month heard how Dhillon stalked Miss Ruggles - originally from Leicestershire - after she ended their relationship.
Seven months on from returning home to find the body of her best friend in the bathroom, Ms McGill, from Glasgow, described how she "froze with fear" at the discovery.
"It was nothing short of a disaster. Nothing could have prepared me. It was worse than what you see in the films," she said.
"From that night I've never been the same. I've always been a strong minded person and sure of myself, but as soon as I saw Alice I froze with a fear I've never felt before.
"I was petrified. Knowing what had happened I was worried for myself, but I knew at that point that Alice wasn't here anymore. It stays with me every day. I'll never be able to erase it from my memory.
"I find it hard to imagine that I'll never see her happy and beautiful smile.
"Life for me is different now from what it used to be. I'm just trying to focus on the basics but I don't enjoy social events anymore because I feel on edge with any new people I meet."
Ms McGill described how she became increasingly concerned about Dhillon's treatment of Miss Ruggles before the relationship ended.
She added: "Over time it became apparent what was going on and how he was trying to turn her against her friends. It got to the point where she wouldn't go out because he wouldn't let her out of his sight.
"Finally she confided in me and told me that while she was in the shower he made her get out and stand wet and naked in the kitchen with shampoo and everything in her hair because he wanted to go the toilet. At that point I told her was never coming back into the flat.
"What type of man would do that, especially to someone you're supposed to love."
The best friend of a woman murdered by her "obsessive" former boyfriend has told how she now feels "on edge" meeting new people.