My girlfriend and I bought a product together and I'm made she reviewed it without me.
Did she not tell you until after the review.
Correct. She didn't tell me at first because she opened the product.
It is okay for couples to do things apart but if both people are looking forward to something, you should talk to each other if you don't want to do it together. It will help to not have hurt feelings otherwise.
Whatever, I'm angry she bad mouthed that product.
It's a bummer your girlfriend reviewed the product without you and I'm sorry she left you out of something you wanted to do. Since you don't agree with her review of the product, perhaps you too can review it on your own and share your opinion.