This is a variation on the Cuckold husband concept. I think the writing flowed and the sex scenes are better than the ones I write. My real complaint is that this is one plot that just doesn't work for me.
My problem is that I've done some volunteer work in a maximum security prison and also in a minimum security prison. The husband would own the guard! In fact this is one of the things that guards are warned about because any contact with a prisoner's family is ground for dismissal and possibly prosecution.
The reason is simple, it's too easy to get a guard corrupted if they start meeting family members.
So, if you can suspend belief... should be easy to do, and if you like seeing a husband humiliated (I have to confess I don't enjoy that but I'll always read any prison story) you'll enjoy this story.