If you put yourself in Nozomi's place, you can't really blame her. For biggest part of her life she did not have friends and never thought she would. And now, the person she loves the most, loves her back. But does she really? Or is Eri just nice and pitying her?
For someone who was alone most of her life, you can't blame her for doubting Eri's feelings. And as was said, hotel was not the first time. Nozomi had tried to seduce Eri multiple of times before but Eri being her oblivious/shy self either did not get the hint or ran away. So Nozomi decided to be straightforward.
Eri being constantly on defending side made Nozomi feel even more insecure than she originally was with their relationship. It's a totally normal reaction, especially for 17 year old teenager. And especially for the first proper relationship.
They are both at fault for not talking things through from the beginning. Eri's fault is that she never explained her reluctance to sexual activities, she just outright avoided them like fire. If she explained herself, Nozomi would not start the whole drama. She would understand and wait.