Red flags all around?

About 3 weeks ago I walked away from my girlfriend of 3 months.

The first month and a half was nice. All lovey-dovey, etc. Testing the waters. Unfortunately, just after Thanksgiving everything went south. She seemed distant and cold, and according to her me staying at her house for a lengthy period of time was too much. Though both of us went to work, on similar shifts. Then the excuse came that she needed her Space. Instead of seeing one another daily, it first went to every other day, to once, to not at all. She was still attached to her ex, with whom she has a daughter, though they were broken up for a year, and was involved in a bi relationship with what she considered her "wife". I was constantly wondering if I did anything wrong, asking her if she was mad at me about something, etc. Then she said I was whiny, clingy, mopey, and needed therapy for my baggage. One of the last times I spent an evening with her, we had gone out to the store for groceries, where she literally bought boxes of cereal for ex to eat at her house.

Being a hopeless romantic, I thought she was going to be the one, and wouldn't play games.

Did I miss the warning, and not see the writing on the wall?