Yep. Reddit is filled with this kind of stuff.
That's what normies are hopefully starting to understand about women being sluts. The likelihood they've encountered a big dick, which are actually rare, goes up the more dudes she sleeps with. And if she's had one of those, she'll never be satisfied with a normal one. There is no special skill in bed better than just being genetically gifted. Simple as.
If he talks to her about it, as many of the reddit hive mind are undoubtedly suggesting, she'll dump him. It will make her use of him for financial convenience and emotional support wholly transparent. As much as anti-incels try to say sex isn't important, the lives of normies reveal how untrue that is. Sex is the center of a sex havers life.
Also, the other guy likely isn't even three inches bigger than him. Very unlikely unless OP is exceptionally small. Women are shit at measurements. It's likely only an inch and a half or so longer. But that's all it takes. Much like the face, a small measurement often separates being adored by women, being just good enough to be used by women or being incel.