I understand, and I know it may be hard to think past that after it appearing so suddenly after so many years. But neither of you were tested at any point in the last seven years, so you can’t rule out that it was there before.

Please talk to her, let her know you are upset and are unsure but that you are not accusing or blaming her. Ask her if she could have got it from anyone while you’ve been together or if it could have come before (assuming she’s had previous partners?). If she cares for you, even a little bit, she should tell you the truth.

But please please please do not just blame her, because if you find out she is innocent she may not forgive you if you’ve accused her