Huge cum stain on marriage bed

Years ago when my wife and I were first married she went back to school to get her Masters degree. She was in her mid forties but still hot. Her pics are on my profile. I worked nights and she was usually off to school or work when I get home in the morning. I slept in the guest room on workdays because it had room darkening shades. My wife slept in the main bedroom and the bed was always neatly made when I came home. This particular morning before I went to bed I noticed it was unusual because our bedroom door was open and the bed was a mess. Upon closer inspection I saw a huge stain in the middle of the sheets, wasn't hard to figure out it was a huge cum stain. I am small endowed and had often told my wife I didn't mind if she took on a younger larger man, but she always gave me the same old line that she didn't need anyone but me.
She had before mentioned there had been a young guy at school that she had made friends with and wanted to know if it was alright if she invited him over some weekend for a cookout. I told her I didn't mind at all. I figured at the time he probably wanted to fuck her When I saw the huge cum stain on the bed I figured he had came over and fucked her while I was at work. My little dick got immediately hard when I thought about some young stud having his hard cock in my wife, could imagine him fucking and cumming in her 3 or 4 times with as big as that stain was. I couldn't help to add my jizz to the mess.
Later found out it wasn't him and it was a young black guy that had fucked her will tell the rest of the story later.