Negative thinking has not sent you into a downward spiral. You are choosing to obsess about your own negative thoughts. If you continue, you will destroy your relationship. If someone loves you, no one can take him or her away from you. If someone does not love you, then you cannot make that person stay.
Relationships are really that simple.
There's no need for you to punish yourself because someone else is attractive. I want you to do a lot of mirror work. I have tried everything from meditating, vitamins, resting, and a healthy diet. Last summer I became ill, and after several misdiagnoses from various doctors, I was diagnosed as having viral meningitis. I have been hospitalized twice, had seizures, taken a course of Prednisone, have tried many strong pain medications, and I still do not have my health back.