Need help finding this movie

It’s so odd but I can only remember the movie very very vividly since I was only about 7-8 years old. I believe it was on one of the movie channels back then, I can’t quite remember if it was in black or white. But in the movie a main character with blonde hair goes to this house to look for her sister, there’s an older woman who lives there with who I believe is her son. At night time, the main character walked in his room and he has iv injected into his arms, he attacks her and becomes violent.

The next day he is normal and doesn’t know anything happened, she attempts to leave taking a taxi, it seems like she’s being taken away from the home, but is revealed that she’s taken back. She ends up fighting the lady of the house who falls through the glass balcony and dies. The guy still tries to attack her and in the basement her sister who was missing at the end of the movie seems to be out of the sorts and attacks the guy, they both land in a box or what appeared to be a tanning bed, she ends up falling on top of him and they kiss.. and are dead? I am so so confused and have been trying to find out what movie this is for many years. I am 24 now and can’t figure it out