First off you have no size problems. I don’t think women care much about length unless its so small it keeps falling out. Everyone talks about length and 8 inches but any talk I’ve ever had with women on this involves girth. In fact I’ve heard a few times that long dicks hurt. And I’ve heard that long skinny dicks are not favored. So that other guy probably had a longer skinny dick which is why it just hurt.
If you have 5.4 mid girth and that is natural without PE or post-PE swelling from an hour of pumping then you are big where it counts most.
Your mind is the problem. You could be 9 inches and still ashamed of your dick if your mind is messed up.
So implant this in your head.
1. The other guy was long and skinny and gave no pleasure just poking and pain
2. You are well above average girth and that’s what women really want
3. You can easily gain half an inch in length from stretching and that would make you about 6.5 x 5.5 which as far as I think falls into the ideal range for women.
Many guys including myself would love to have started at 5.4 girth so understand that you are lucky with your starting stats.
And do not talk size or show major insecurity as it is a bigger turn off than a micropenis to women.