Our two cases are very similar. I am able to ejaculate only the first few times I am with a woman. Then I find myself getting bored and the RE problems start. When I look at porn it's the same thing. I can't watch any given movie more that once or twice without getting bored.
I think some people just need a certain level of excitement during sex which isn't possible once a relationship gets established. The old saying "familiarity breeds contempt" rings true. Although I would reword it as "familiarity breeds boredom"
I have been in alot of different kinds of therapy over the years and have come to believe that my sexual perference for newness is just who I am. It has made a mess of my marriage because I too suffered ED and the inability to ejaculate with my wife and this started a few months after the wedding. Instead of being fun, sex became a chore and was very stressful. I did it to keep my wife happy. I told her not to worry about me and that it had nothing to do with her. I can give her orgasms orally and with my hand but I get nothing out of it. I like being married which is why I stay on. Plus I know the same thing would happen with any other woman.
When I was single I just broke up with the woman and moved on once I got bored. Now I feel trapped sexually and porn and masturbation is my only outlet. The great thing about porn is the constant variety which mimics what I had before I was married.
Psychoanalysis may help me understand why I have a sexual preference for newness but I doubt anything can change the preference and cure the retarded ejaculation and erection problems. I have none of these problems when I masturbate by myself. I have tried moving the porn and self masturbation into sex with my wife but like most women she doesn't like porn, or at least the kind I like (lots of anal, black and asian women, multiple girls on one guy) and the so-called "couples" porn out there leaves me cold.
I have learned to live with the situation and that's the best alot of us with RE can hope for.