[MOVIE] I’ve been looking for this movie for years and can’t find it. Please help!

I watched it online around 2016 or so (probably before that). It was in English.
It’s about a boy who lives with his mother. He has a girlfriend (a brunette girl, kind of dark-skinned).
One day, he gets angry and kills her by smashing her head.
Then, his mother takes the body to a chamber with black liquid, submerges the girl in it, washes her, and brings her back to life — but she doesn’t remember anything.
The boy does this over and over: kills her, and his mom revives her.
But eventually, the girl starts remembering little by little…
In the end, she kills the boy and escapes.

I remember the film showed how they met, and some of their relationship before the killings started.
It looked kind of low-budget or indie.