Your friend is going through needless trauma that is purely a construct of his own mind, beliefs and perceptions and such. Warts are no big deal and to be affected this much by this is not cool. In the past I've been really sympathetic and I am right now too, but you need to tell him to buck up and grow a pair and face it down. HPV isn't a terrible STD to have, he needs to do research and understand the virus and know it's just a skin condition that happens to be on your penis. To abstain from sex for six years because he's not getting informed is a travesty of life if you ask me. For the life of me I have never understood that kind of behavior as the very first thing I did was learn all I can about it, at least where men are concerned.
I don't know why they haven't gone away completely yet. Most warts resolve on there own in less than three years even without treatment I've read. I have zero knowledge on this though. With treatment you can expect up to two years from start to finish before you don't get any recurrences anymore.
My recommendation for him is to stop stigmatizing himself. He needs to realize that nearly everyone has this. I have friends who are poly amorous and they all sleep together and sleep around. IT's crazy how promiscuous they are. I chatted with ehr about warts and HPV in general the other day and she said that it's just assumed you have it or had it and no one even talks about it is that common. It's less common for "regular folks" such as ourselves, but it's very very common. You get it, you treat it, you fight it off, you move on. So, get your friend into the doctor. If you want, have them remove it and send it in for a biopsy if he want to know for sure it's a wart. Usually people aren't contagious after six years but since it's still there I don't really know. Go to the doctor and buck up some courage and the will to learn the facts. That's the best offense. He can do it. If he's scared or depressed, talk sense into him and pump him up until he does. Good luck.
i've been doing researches myself, including asking different dermatologists and doctors from STD clinics in real life. HPV is something you would get for the rest of your life, indeed, but your body may be able to force it to go dormant (after 6-24 months of initial infection).
However, there's no definitive answer to whether someone can still infect his/her partner even after he passed that 1-2 years period. The possibility will be always there but way smaller i believe. Also you have to keep in mind 1-2 years period timeframe is just for 90% of people, 10% would take longer time like 3 years or 4 years or maybe even unable to fight the infection for the rest of his life although the chance is very small for this one.