Human Angle: How can I stop having sex with my brother-in-law?

I think I have had it enough, and it’s even becoming more habitual as I always have a fast one with him even when my husband is in the house. My fear is that my husband will soon understand the gimmicks, if we continue in the escapade.
I’m very sorry to say this, but I think I’m an addict, as I get to my pick when I cheat on my husband. I also enjoy it more when it’s done swiftly; just that alone satisfies my libido. However, the reason why I’m so attached to this guy is because he is a complete man. No man can do what he does to me; in fact, it’s unspeakable.
When I met my husband 10 years ago, I knew he was my kind of man, as he was able to satisfy me the very night we met. We both met in one of the universities in the North. We got married just 3 years ago and here I’m trying to battle out of some addiction. I know it’s shameful, but it’s really hard for me to fight.
I had vowed never to be callous to him in any way until his younger brother finished his University program and came into our house last year. Two months after he got into that house, the entire story changed. We had our first night when my husband went on an official trip. I can’t give you the details of how it all happened, but it was the most regrettable night, as I regretted my action after then. We both concealed it, and pretended nothing ever happened, but from that moment, and even as my husband returned, he has not been able to satisfy me the way his brother did. This has kept me glued to his brother. Most of the time, I sneak out of bed to the toilet at nigh where we normally meet to do the dirty thing.
I will deliberately wake my husband when he is at the pick of his sleep, informing him that I was going to the toilet. I would always make sure I get back to the room within 5 minutes, but I tell you, I often return satisfied.
I’m gradually losing my joy and dignity as a married woman because of this development. It’s even becoming a daily occurrence, especially now that my shop has been closed permanently due to the ongoing crisis around my area, and I’m always at home with him in the morning. In fact, even as I write this note, I just doubt if we won’t have it the whole of today. I’m really not happy doing this, and I can’t even tell my husband. I know that the very moment he gets hold of the truth, he will throw me out of the house. I won’t tell him, I will protect my marriage. The brother is just so comfortable with what we are doing, as he has never discussed the negative side of our rough game with me. But the problem is that, at the most quiet time, especially when we are alone, and we look at each other, we just can’t stop doing it.
What is the solution please? is my case medical, spiritual or biological? I need your candid advice. I need to find a solution as I cannot continue like this, even as I don’t have a clue.