Backing up some other thoughts - most often when a girl is off sex, it has nothing to do with your dick. It's usually something that she's going through independent of you, or something about your relationship with her.

I think that it's sometimes hard for guys to get that the desire for sex, or lack thereof, isn't necessarily about how it feels for women. I mean, that can certainly affect sex drive. But frequently we aren't in the mood because we're stressed, tired, worried, or feel something in the relationship is off. Similarly, frequently we're horny as anything because we're feeling secure, relaxed, happy, and well loved.

Don't worry about your dick. The only time penis size has ever put me off was when it was too LARGE, and even then there's a wide range of wonderful size. Take the time to examine your relationship with her and her emotional state instead.

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Thank you, sir, may I have another?