I have a story related to this a little.
I have a pretty average size dick, it's not big or small just average going off my years in sports teams, feedback, etc. I moved to a new city for work when I was young and lived in flat opposite a group of catholic university girls who were from the sticks like me and naive as hell as far as sex goes. Anyway one of them took a fancy to me and had her friend slip a birthday invite under the door. The main thing here is they were going to McDonalds and hiring a male stripper. I probably could have had a good night with a bunch of horny drunk girls but I didn't want to hang the whole night at McDonalds and then watch a guy get naked, so I blew it off thinking I was pretty much a certainty anyway and went home for the weekend to party instead.
Fast forward about a week and a half, I get this girl alone for a bit and she gives me head but wouldn't take it any further yet. The other girls(especially one who obviously liked me as well) started acting very weird towards me after this saying they "know" about me and what a shame it was because the rest of me was pretty hot. I'm like, wtf is this? Anyway I get this other one alone for a bit and she confesses to me that her friend had told them all I had a tiny penis. Back then the internet was pretty niche and the only thing this girl had to compare me to was the Johnny Holmes wannabe who had stripped for them. So the story got around that I had a tiny cock which I probably did compared to him.
That all ended in a mess because I actually ended up sleeping with the second girl and told the first one it was because she'd spread rumours about me and that caused a big argument between them and they all moved out. I had a bit of a relationship with the second one until she turned up one night while my ex from my home town was staying over. So all my wells dried up right there in one hit.
See the top comment for the previous story.
If you're married, a lesson you will learn early on is that you need to keep your internal issues between yourselves. The other will find out that you talked to someone else about it and it will blow up in your face.
That said, the subject of this story is also the asshole and should have manned up and disclosed it beforehand. Regardless, you don't do what she did, never ever unless you're trying to get a divorce. You might be able to talk to others after it's resolved, but make sure it's resolved before you head down that path.