Help! I'm in Love With My Husbands Brother

I have a problem bothering me, and I hope you can help me. I am married and love my husband, but I have a crush on his brother. His brother is a Doctor and has a terrific body.
One weekend he came to the house to visit. He was there for two days. He is great with children. The Saturday evening he was in the yard playing football with the kids and took off his shirt. When I saw his body, especially his abs, I almost went crazy. I kept staring at him. He is very strong and sexy.

That night when I went to bed with my husband, I asked him why he can't look like his brother. He was surprised at what I asked him. He started to laugh and, in the morning when we woke up and were around the breakfast table, he told his brother that I was in love with his body.
His brother asked me then and there if it was true and I was embarrassed. I told him I saw him with his shirt off and I loved the way he looked, but there was nothing more to it.

However, every time I think of my husband's brother, I am tempted to call him. I don't know how he would react. He and my husband are very close, so he may tell his brother that I called, and I don't want that.

Making love with his brother
When I met my husband, he didn't have abs, but he was in good shape. Now, I can't get him to eat right. He eats a lot of junk food. He does not exercise. I can't get his brother out of my mind. I can't understand it because I have never thought of cheating on my husband. It is very bad because, even while making love with my husband, I am wondering how it would feel making love with his brother with those lovely abs and arms. I am not joking. I wonder how it would feel. I know what I am doing is not right.

One day he called the house to talk to his brother. He was not there, so we talked for a long while about everything, including his girlfriend. This time I fell in love with his voice. He is so intelligent. I was answering the phone in my bedroom. While I was talking to him, I started to fool around myself. He knew I was doing something because he heard me gasping for breath. He asked me what was going on and I told him nothing. He suspected what I was doing, so he hung up. Is this normal?
My husband and I have a good relationship, so why do I feel this way about his brother?