She sent me a text

Wow..... she sent me a text stating she is his wife and needs to know from me if anything is going on between us and to please respond with the truth.
I freaked.  I kept thinking.....if I dont respond she will assume the worst, they wont get any sleep and it will be fighting all night.  And even if she isnt convinced she will have an answer and at least she has something she can choose to believe in.  And obviously he is saying nothing is going on so our stories match.  
She responded that she hopes nothing is going on and it really hurt her to see my text and thanked me for responding.  
Looks like a crisis is averted.  This could have been soooo much worse.  There won't be a next time.  I'm going to change my number.  I can't believe I have done this to someone else.  I know what it is like to love him and how much her heart must have been breaking to think he cheated on her.  
I'm not a bad person- I'm a good person.  I dont know how I got here but I think I need to figure it out and find a therapist.