Is she playing me for the fool or am I losing it?

I've been dating a girl for over three years. We lived together for two years, and now we are back from college. I'm living at home and so is she until we have enough cash to get another apartment. She recently started a new career as an accountant.

A month or so ago I found out she lied to me:

We had been hanging out on a Thursday night and she said she was going home and going to bed; it was 730 pm. This was weird, but I let it slide, I've been with her for 3 years, why question her now? A few days later I was surfing around on Facebook and found out that she had (publicly) made plans with another guy to go to a movie. This guy and her are old friends, they hang out and go to movies together a lot and she tells me there is nothing to worry about this. I was mad that she hid it from me, but willing to try and deal with it. She promised nothing like this would happen again...

So, fast forward to the day before NYE: We are at a party, and I borrow her phone to use the internet on it (her browser app is way faster than mine). She happened to leave her Messaging app open and sure enough, 7-9 casual texts to some (different) guy. I ask her about it, naturally. She says it's nothing serious, just some guy she used to work with back in college who came down and invited her out to coffee. She said she wasn't interested him and he was "way too old". When we first started dating she told me she was into a different type of guy than me (muscular, blond, blue eyes), and sure enough "older, dark haired, dark eyes, thin, etc." the shoe fits.

I am so lost in this situation. We are less than a month from getting an apartment together. She is taking her CPA exams and working full time at the same time, it would seem completely unreasonable that she would be cheating, or even have the time to do so, but I looked up some things online about signs of a cheating partner and she fits like 80% of the criteria:

-absorbed with her phone around me

-lack of sexual interest (it's been months)

-defensiveness (accusing ME of cheating)

-spending (way) more time at "work" and "studying"

- having many new friends

- focusing on her appearance more

-constantly prioritizing me lower in her time

-using distance as an excuse when before it didn't matter at all

Every time I try to talk to her sensibly about it she accuses me of not paying enough attention or not listening to her. She says that it's all my fault. Every time I ask her if she wants to break up with me or take a break she just cries and makes it seem like I'm the one creating the problems.

Ive honestly been trying as hard as I can to please her and be there for her when she is stressed. I feel like she is cheating and hiding it from me, in the pit of my stomach. She denies everything, but the evidence is ever surmounting. Am I losing it and fabricating all of this? Or is my girlfriend playing me for the fool?

I just want her to be happy either with me or without me. I'm not OK with open relationships or cheaters.
Is she playing me for the fool or am I losing it?
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