I lost my moms wedding ring, and it ended up being the root cause of her divorce
Are you sure that losing the wedding ring was the main reason for your mom's divorce?
Maybe I did cause the divorce by losing the ring but it doesn't bother me.
You have not been honest with your mom about losing her wedding ring. You should talk with her and tell her the truth about what happened and be apologetic.  If she finds out some other way that you have lied to her, then she will not trust you in the future
Nah my mom will be fine, don't worry. She's moved on.
Well, if your mother has truly moved on, then maybe it would just cause more pain to bring it up again.  From the way you describe the situation though, I'm sure that a lost wedding ring was just the last in a series of problems, so you shouldn't fully blame yourself.