I'm not disclosing my infidelity to my wife who's now sick
Why won't you tell her?
I don't think she will outlive finding out.
It is wrong to lie and cheat on your partner. You should be honest with them or never tell them and stop cheating immediately.
Not telling a lie is an option but in reality I'm not going to do it.
It is still wrong to lie and hide something from your dying wife. If you don't feel like telling her you should stop and keep it a secret and support her until she passes.