Testify.
Otherwise, you will likely feel bad later on. It is not just how you feel now, but how you will feel in the future that you should think about.
And also, I am sorry that anyone has to deal with anything like what you have to deal with. And if someone has to deal with this, it should not be you.
Think about what you believe is the right thing to do. I think you should testify, and tell the truth. It will hurt, and I am sorry for that. But it will also hurt in the future if you now do what you later on will regret.
Otherwise, you will likely feel bad later on. It is not just how you feel now, but how you will feel in the future that you should think about.
And also, I am sorry that anyone has to deal with anything like what you have to deal with. And if someone has to deal with this, it should not be you.
Think about what you believe is the right thing to do. I think you should testify, and tell the truth. It will hurt, and I am sorry for that. But it will also hurt in the future if you now do what you later on will regret.
"A wise man ... proportions his belief to the evidence."
— David Hume, An Enquiry Concerning Human Understanding, Section X, Part I.