I feel a bit sorry for him (and you too, of course). He does things to help around the house, can't keep an erection, so watches some porn, but you think he's up to something with someone?
The hair could have come from you, surely? Has he given you any real reason to suspect him of having an affair? If he has erectile dysfunction, would he be able to have an affair?
I wonder if the porn issue and the lack of sex are contributing to you feeling insecure? TALK to him. Invite him into your bed, get close, without sex, and see how things are. If you both think you'd like to have an active sex life, get some Viagra (you can buy it now, I believe)