She got very upset and I didn't have the heart to leave so I slept on the couch. This morning I told her to make an appointment with her therapist today and start preparing to be alone.
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I'm not sure if there's a constructive way to say this, but I think you are the one who may want to talk to the therapist. If someone telling you they brushed their teeth when they really didn't can hurl you into that kind of rage, are you really prepared to own a house and live with another person? In most relationships, there are problems/issues to work out that are much worse than whether or not your partner brushed her teeth.
And why on earth would you be checking her toothbrush? That just seems kinda odd to me. I wouldn't want to be with someone who is constantly spying on/questioning my every move.

hc