Small penis or large penis, if it's got a big open sore on it, it's a turn-off. Small penis or large penis, if it's been severed and has flies buzzing around it, I'm similarly going to have to go with it being a turn-off. Small penis or large penis, if it's limp and the situation calls for it to at least be getting hard, usually a turn-off. Small penis or large penis, if it's attached to a dishonest jerk who lied and told you he's not married or in a relationship, it's a turn-off. See a pattern? Not the size that determines whether it's a turn-on or turn-off..
My wife found my three-and-a-half-incher quite sexy when we weren't quite as old as we now are. Back when I was about 19, I "did it" many times with a girl who had no complaints about its shortness. Not sure about other women, but I know some men find the sight of it exciting--especially when I'm showing off my shemale self!
It's time to stop letting your penis size ruin things for you. 5 inches isn't even that small. 3 and a half inches (like mine) is small, but it hasn't ruined my life by any means. As for inability to get an erection: there are medical treatments for that sort of thing, but the "treatment" I used when I was finding it hard to get erections for my wife some years ago was to return to the girlish pretensions that greatly excited me when I was a teen (beginning at "zero-teen," 10 years of age). I did get erections, all right, although I also got a strong desire to show off my newly rediscovered shemale self to men on the Internet! If the things that gave you erections as a teen no longer do the job, you might want to ask about some medical assistance.