well, u could get her too put the condomn on u with her mouth and that would probably keep it up... or if ur not trying for kids get drunk then u wont be so worried about it. also u could use viagra. sure u could get an erection but viagra would make sure u kept it

This has got to be psychological. Which is great, physical issues are much harder to get around sexually and I've never heard of any sexual response that sounds like what you're describing. It really does sound like the extreme version of performance anxiety. I'd start by checking any medication you're taking for possible sexual side effects and discuss the problems you're experiencing with the doctor that proscribed them. If you had a traumatic experience with your wife around the time this started, a fight after or about sex, a health issue during sex it could be that you just need to "get back in the saddle" don't pressure yourself to perform, work up to sex with other intimacy until you both are comfortable. If what's going on is more obscure, less easilly tied to the bedroom there's a lot of fairly nasty things your mind can do to you in bed. You may end up needing to see psychologist or if your wife will go, take her to a certified sexual therapist.