@Circle rainbow ,
Yes, he's having an affair. Check his mobile phone, and you'll probably find the evidence. (My wife did all the same things, well almost all)
Per your suspicions:
Not wanting sex? Yup, he's having an affair. Unless there's something wrong with him, he'll have some sort of sex drive at his age.
Picking fights? Yup, he's having an affair. He's hoping you'll say you don;t want to be married anymore, which gives him an excuse.
"Needs space" Oh, the number of times I've heard that one - both with my wife and friends who have had the same experience. Classic affair talk.
No intimacy? Of course, he's getting it somewhere else.
Phone to shower: I don;t know too many people who take their phone into the shower, so to me this points to the fact that he's communicating with someone and he does not want you to know. Does he have a password to access his phone? Yes, that's classic cheater behaviour as well.
Change of dress: Classic cheater.
Dry and peeling penis: Does not sound like an STD, but he should get it checked out by a doctor.
Sorry to say this to you, but, if I was you, I'd buy a cheap phone, install a geotagging application and a voice activated recorder application (all available free) and hide phone in his car - Under the seat is good, but make sure it can't slide out. Then you can use GPS to track his movements and, you'll hear any conversations he has in the car. Of course, you will need to keep charging the battery, so need a bit of work and stealth to pull off.
Check out his mobile phone. If he's defensive and won't allow you to use or play with his phone, then - sorry - there's something on there that he does not want you to see.
Could be, of course, he just has a bad porn habit, but apart from that - I recon there's nothing wrong with you - you're absolutely correct in your suspicions.
Good luck!
My wife and I are slowly working through the damage her affair caused us. If you love your man and you want to fix this - do so now. Otherwise, be prepared for the eventual split-up.