Originally posted on r/Advice, but I'm cross-posting here for broader input.
I (28M) just recently started using dating apps after never having dated before. As I was "scrolling" through Hinge today, I came across the girlfriend (29F) of one of my best friends (29M), who have been together for nearly four years and living together for three.
I'm a little hesitant to assume the worst, as, the other day, I was hanging with my friend discussing online dating, and he made a joke Tinder profile to "see how many likes he could get" (it was an obvious joke profile, with non-serious answers to everything and Gigachad as one of his photos etc.). I therefore wonder if he could have gone home and had the same conversation with her, where she also made an online profile so they could compare with each other. However, I find it strange that she would choose a serious app like Hinge and not Tinder (the platform through which they met each other). I never even disclosed that I am using Hinge to them.
At the same time, the girlfriend is fully aware that I am on dating apps, as she was even giving me some advice about how I should go about asking girls out, given my own lack of experience. I kind of regret immediately pressing X on her (the Hinge equivalent of a left swipe) and wish I'd taken a screenshot. Her profile seemed pretty serious, though I didn't spend a huge amount of time looking at it. She also had her name set as the first letter of her name, rather than her actual name. I'm also aware the some couples agree to use dating apps to explore polygamy, but they really don't seem like the sort of people who would be into that.
I'm torn about what to do. On one hand I would like to keep out of any internal drama they may have. I even question if it was simply a look-alike, who just happens to have the same initial and age, but I think that's just coping on my end. On the other hand, I feel shady keeping this information from a close friend.
TL;DR: Saw my friend's girlfriend on Hinge, it may or may not be innocent and I don't have proof, I'm not sure if I should tell him.