He's got psychological or physiological problems he doesn't want to deal with, that simple.
I'm sure somebody will weigh in in the comments about how "asexuality is a valid choice", and it is: if you genuinely don't want sex, you don't want sex. But bluntly, it's like Asperger's: the number of people claiming to be asexual is a much higher number than the number of people who actually are asexual.
Generally, if somebody is claiming they don't need sex, they're avoiding something. They could be gay and not want to deal with it, they could have a trauma in their past they're doing their level best to ignore, they could have an abnormally low sex drive for medical reasons, they could have body image issues...the list goes on.
Either way, five years of this crap has got to be hurting your friend. If he's making her miserable and insecure because of his issues, he is not a nice guy. Tell her from me to dump his ass and find somebody that makes her happy.
Yipes. That is not normal. :(
Ultimately the why of it isn't really that important. What is important is that she's thoroughly miserable. I think 5 years is more than enough time for them to come to an agreement or try to work through whatever issues there may be and it hasn't happened. So I say move on - don't waste any more time in a loveless/sexless relationship.
If he's asexual or gay or whatever the reason is, he needs to be honest with her and himself and let her go. Their living situation is not one of romantic partners. They're friends at best. It is cruel of him to keep her hanging on.
After 5 years, if he's not getting it from her, he's more than likely getting it form someone else- man or woman.
It never ceases to amaze me how much women (myself included) are willing to excuse with the phrase, "but he's really a nice guy."
Sometimes, I have to remind myself that being "nice" is the bare minimum. Your friend should do the same.
I was with a guy for just over a year who didn't want sex. His excuse was it "created too much commitment' and he didn't want to go there...but we slept in the same bed AND cuddled when I was there every weekend. I have many gay friends, and DID (sensitively) ask him if he thought he might be gay, and he said, 'no, not even close'.
Your frustration must be even more than mine after so long, but I did keep the communication clear, respectful and kind.
When I broke it off with him, I was very upset, but said that
"affection, and showing love physically, is something that I (we all) need for comfort, and I deserved that in my life. It's something that most people NEED to build together to have a complete relationship.
If you're not willing to 'go there', or talk to a counselor about why you don't want to 'go there' so we can move forward, I will need to move on from us.
It makes me feel sad and empty, because I love you, but just as you deserve to be happy and fulfilled, so do I."
Hope some of this helps you to think through this difficult situation.
Best of luck in whatever you choose to do.
OR, they could actually be asexual. -__- One of my best friends is genuinely asexual.
That said, if he is, and she isn't, staying together probably isn't the best idea. They have totally different needs.
I would never last that long...
nice guy or not, she needs to move on or its going to continue doing damage. does she think she can put up with that for 10 years? how about 15 or 20? If its been going on for 5 i don't see it changing. If she needs more affection shes just putting off the unavoidable and making herself miserable in the process.
tell her to gently dump him, get a bf with a sex drive and go at it like rabbits(with protection of course) to heal the past 5 years. let him go on his asexual way.