I had one close friend in college who dated a guy for about two years. She was notoriously promiscuous, he had a slightly smaller than average penis. She preferred big dick, but she wasn't a size queen - she loved fucking him. She was loyal, and she was ready to marry the guy. I liked him and was happy for them.
His insecurities (about his dick and other things) chased her away. This isn't "her side of the story," either - it's observation. I watched this guy become overprotective, suspicious, jealous, and annoying over time. She dumped him when it came pretty close to him fighting an ex boyfriend of hers over nothing. Still, I hung out with the guy a bit, because he was otherwise fun to hang out with.
Their breakup worked out in my favor, because she and I had been friends for years but it was a few weeks after that relationship that we first had sex. She told me after the first time we fucked that I made her legs numb for the first time in years, and I mentioned that I think it was my length - I noticed her enjoying when I hit her A-spot. She agreed, and she told me sadly that the ex boyfriend (and most men she had been with) couldn't hit that spot. I gently suggested that, although I love talking about the past, I didn't want to know specifics about guys I knew, and she said something along the lines of "I'm sorry, I haven't been able to unload that frustration...he was pretty small, like 5 inches and thin. I loved it, but yeah, this is better," and stroked my half-hard cock.
I obviously felt great about pleasing this woman and giving her a size she wanted, but damn...I felt so bad for that guy, and I basically told her never to talk about his size again, to anyone.