I'm having an affair with my step son
What is causing you to have this affair?
A feeling of lust and temptation led me to do this
I understand that lust can cause bad decisions, but this behavior is hurtful to your spouse and treads into unethical.
I don't care what others think.
It is not about what others think, but how you are hurting people. You need to get out of both relationships and start fresh.