I think you answered your own question, david.lu,

Until your wife stops "just laying there" and expect you to do everything, your sex life - and your erection - won't operate as you want it to.

One of the issues is surely the "emotional conflicts" - things said during arguments, even if only in the heat of the moment, can demolish a sex life into complete oblivion. All the roses in the world won't change the fact that you feel sexually belittled and short-changed.

I don't know what the "conflict" was all about, but clearly your wife feels bitter about it and is now punishing both you and herself in the process. Hence, you have both resorted to one-sided sex; you through masturbation, and she in getting serviced by you.

My guess is that the bitterness is going to shift and eventually you will begin to feel very resentful [maybe you do already?] about always catering to her. The most reasonable thing at this point would be for you to enter couples counseling with a competent sex therapist who is also skilled at marital therapy so that you can discuss the underlying issues. They are not going to go away and they will get worse if you don't start talking them out. Until then, sexual mutuality may elude you.

Go for counseling if you want to stay authentic in the marriage,
The Love Goddess

Dear LG,

I’m 37, physically healthy. I have no problem of maintaining erection when I masturbate (I can last 30 minutes or more with hard erection). But I can’t have intercourse with my wife. The thing always goes like this: I get erection during foreplay, but before intercourse, I lose it. Part of the problem is the foreplay is one-sided. My wife just lay there and expects me to do everything.

The whole thing went worse after many times failure. Now my wife is unwilling to let me touch her. And occasionally when she is horny (usually the day before her period), she allows me to try but again I failed to enter her.  It’s becoming a try-once-a-month-and-fail then no-touch-for-the-rest-of-the-month situation, very frustrated.

We had very good sex before we got married. But in recent years, after some emotional conflicts, our sex life is very low. I’m trying to work it out: I sincerely apologize to her for the past hurt; buy her roses every week; kiss and hug her every morning and evening. Our relationship is getting better now. We just celebrate anniversary and we verbally told each other we still love her/him, but we still can’t have sex.

Any advice is highly appreciated.

I second the motion!  I have had a very similar situation despite marriage counseling.  It is very hard to revive a sexual relationship where emotional damage has been done to the relationship.  My wife and I have both been in individual therapy as well, which has helped a great deal.  I strongly suggest you take LG's advice and get couples therapy as well as sex therapy.  A long-term sexual relationship can only sustain itself when there is trust.  We are still working on it, but there is hope.

...with them?  If not, what are you doing on TER?

Well-expressed, inicky46.  Most good couples therapists can also help with problems involving sex.

I think the value of individual therapy is often overlooked. It may actually prove to be as useful or more useful than the "couples" therapy

I'm not surprised that you have a loss of erection.  You are not getting anything out of it.  No return participation.  No enthusiasm.  No action.  She's just laying there soaking up all you give but giving nothing back.  

My first marriage suffered an emotional/sexual  trauma actually before we were married.  I loved her & tried to be the loyal loving husband... but the relationship never recovered.  I bought her flowers, gifts, & gave her everything she wanted.  She stayed as long as I was a meal ticket, when I was reduced to bankrupsy she bailed.  
I wasted 5 of my best years with someone who did not love me back...  my biggest regret.  I suffered a major health issue with permanent repercussions before I was divorced.  The emotion hurt was more than the $100,000 it cost me.  

Quit being a door mat, except for occasions, skip flowers.  It's overboard.  It's not getting her to let go whatever hurt she is carrying.  In fact, it may even reward holding onto it.  It's not working, try something else.  
Be a good person...  be the kind of person someone would want to be with.  Be kind.  Try to keep a stress free environment for both of you.  
   
Begin couples counciling with the very best available...  Go yourself first, alone.  Then get her to go, alone.  Then joint to discuss issues.  I would not encourage partner-sex until the emotional issues have made progress.  
skb

If you were reasonably successful with other women, that pretty well nails the sexual problem to the relationship.
YOU will benifit from counciling which should guide you to decide what kind of person you want to be...  
You need to explore your wants & needs.

Then your wife needs to do the same...  and then see if they are compatable.  They might not be...  but then again they might...  with work.  Do not leave any stone unturned...  or you'll forever regret it.    

As I proved already, loving her is not enough...  if she does not love you back...  or is unwilling/unable to commit to a full relationship.  I know people who "settled" (my description) and are now trapped in a sexless marriage.  I (personally) would find it impossible to get all of my life satisfaction without a love life.  

I sincerely hope that you can find a common ground to build your relationship anew.  
skb

Yes. I've seen several providers. I did pretty well with providers.

But then I feel guilty. I still want to restore my relationship with wife. I think the sense of guilty also contribute to the sex problem with wife.

Thanks a lot, LG. I will take your advice.

Thank you, shudaknowbetter.

...except i'm over 50 & married >20 yrs.  I started seeing providers because I thought it was somehow my problem.  It was not.  I realized that over the years, my wife (who calls me "selfish" when I ask for what I need in bed), has been used to me giving her sex whenever she wanted it (not very often), in exactly the way she wants it, and me being ready for it whenever.  So when I couldn't sustain it, and I "blamed her" by suggesting she do more for me, she got pissed, and insisted I see a Dr. for ED meds.  What was I going to say..that it works perfectly well with other women, with multiple pops in an hour?  So I went to the dr, got the Cialis sample, tried it, and still have trouble with her.  I would take it sometimes in advance of what I think would be the right time, and she isn't interested.  So I waste the ED meds on her.  But the stuff is AMAZING to help overcome lower sensations while using condoms!

I should get divorced, but life doesn't really allow that right now.  Lots of families are in the same boat, and I am sure more than a few men have the same story.