Re: lack of sexual pleasure
You don't really provide a lot of information to go on, but I'll have to say I'm stumped on how to answer you..
You're getting aroused and erect, penetrating your wife's vagina, so the sexual act is obviously feeling good, stimulating your penis and making you climax. You also say you don't mind pleasing your wife. There is bound to be something you're not enjoying, rather not getting. Do you ejaculate prematurely often? If so that could be the problem, because when a man can't enjoy the sex act for no more that a few minutes, that can create a great lack of fulfillment. Is there something else subconsciously that you want sexually that isn't being fulfilled? Is there perhaps a type of sexual act or anythig else that you want from your wife that she's not providing? Has sex grown routine and dull to you?
I wish I could help you pinpoint your problem more. Just ask yourself honestly what it would take sexually to make you really aroused and make things the way they used to be. Any hidden desires? Anything at all..
Wish I could help more. Keep in touch and I hope things get better for you.