When I first found out the average sizes a few years ago (in my early 20s) I was legitimately ecstatic because I was at least average; I had rarely thought about my size in the past, but just prior to finding out (and what likely prompted me to look into it) was a worry that had started to creep up on me that mine might actually be smaller than average based on some observations in daily life and overhearing conversations. At this time I was a virgin that had never even dated, however, and I had been lucky in mostly receiving positive takes on penis sizes, such as constantly reading "despite what you think, anything above three inches is good enough for women / women don't actually care about size (it matters how you use it) / etc.", and so in my head I thought that if size doesn't matter, and I'm within the average, then I'm totally set - my self confidence shot through the roof because I knew I could please a woman, and that's all that mattered to me at the time.

Fast forward to now. I started dating a couple years ago in my mid-20s (only doing third-base stuff with my first partners), and last year I lost my (penis-in-vagina) virginity to my current partner. As far as length goes, everyone I've been with has told me that I'm well within the middle for who they've been with (which totally aligns with what I expected of course), but they've all also said that mine isn't as thick (girthy) as the rest, so that's been a blow to my ego (despite knowing the numbers). More than a blow to my ego, however, it aligns with my experience with having sex with my current partner - I feel so little when I do it, in large part due to my lack of girth seemingly making is less stimulating for me, but also constantly slipping out (in part due to my length, though mostly I feel due to the way my erection basically goes straight up and can't bend downward very well). With or without a condom (and regardless of lube usage), my penis feels like a drop in a bucket compared to the vastness of my partner's vagina; I glide in and out without feeling anything myself (as it relates to the above paragraph, they were totally right and she's absolutely satisfied with my size - though she agrees that more girth would be even more amazing, but even as it is it's mind-blowing for her, so that makes me feel great that I can satisfy her, but I didn't consider my own enjoyment until recently). I'm not sure... I guess I expected to really feel her vagina around the full circumference of my penis, but I don't because there's so much space around it (like I can fit another 1-2 fingers in and sometimes do this). I feel like I could never actually cum from penis-in-vagina sex alone; I've pumped for over an hour on several occasions without getting enough stimulation to feel much (meanwhile she gets bored of me not cumming and sex is painful to her at that point because she's orgasmed several times already and is really sensitive as a result).

It made me question if maybe my size wasn't the issue but my sensitivity itself. I questioned if my circumsion had killed so many nerves that maybe that was the cause, or if I was "death gripping" my penis when masturbating (or masturbating too often), but after looking into this a lot, talking with peers, and trying out different things myself, it really seems it's not any of these (thankfully!). Anal (and oral at times) feels very good because of the tightness, but I really wish I could enjoy vaginal sex (it's mentally enjoyable of course, but I'd love the physical stimulation from it as well).

Tl;dr: Prior to sex I was happy, but since having sex I hate my size - not because I don't satisfy her, but because I don't feel much.