Dude (you REALLY do need to get a better screen name),
I've read about your background - that was tough - but... everyone has had some kind of childhood problems. Very few men (or women) don't feel they have some kind of inner unhappiness or wound or hole inside them. It is these issues that can sabotage our adult relationships - if we let them.
A painful but very necessary lesson I've learned is that a man can't look to his wife for love he didn't get from his parents when he was a boy. He mustn't expect her to tend his childhood wounds. He has to do that himself. He has to fill the emptiness inside himself. Once ful(l)filled, he can then love his wife from strength and want and desire, not weakness or neediness or fear. If he's with the right kind of woman, he will then get womanly love back.
I see definite positives in your situation - despite your difficult start, you have a job, a wife and children. You write honestly and do have insight into your current situation. And you do want it to improve.
But you clearly suffer from low self-esteem, see yourself as a victim, and are disconnected from your inner masculine spirit. I very much used to be in that (mental) situation. The good news is that your problems can definitely be solved - IF you are willing to take responsibility for yourself, work HARD, and do the things I suggest for YOURSELF first and foremost. By that I mean that you must not improve yourself in the hope that your wife will "reward" you with lots of sex (you probably know that that kind of thinking has got you nowhere, but I emphasise the point).
What your life must be about from now on, is being the best man you can be. If you conscientiously set about that task and STICK to it, you will inevitably alter the dynamics of your marriage, your relationship with your children, and probably every other relationship you have.
I'm going to post again with some more ideas, but for now there are four things I want you to consider:
(1) I wouldn't normally suggest this, but have you had therapy or counselling for your childhood issues? In other words, have you had these wounds tended by a professional, or are you expecting (even just subconsciously) your wife to do it for you? Sex makes a lousy bandage. Think about it.
(2) I understand you are probably filled with all kinds of fear at the thought of changing yourself, of confronting (and being rejected by) your wife. But fear is an integral part of human existence, and a man must learn to confront his fears if there is to be joy in his life. The very worst thing that is ever going to happen to you is that you will die. Well, you're going to die anyway, right? Its guaranteed. So, your immediate concern must be how you're going to live up until that inevitable moment of death. And it makes no sense for fear of lesser things than death - disapproval of others, rejection by your wife etc - to stifle you.
(3) This next thing is going to sound a bit weird. Start smiling frequently. When you feel depressed and unloved this is the last thing you feel like doing. It feels forced, even fake. But the very act of smiling does actually release certain chemicals which have the effect of lifting the mood. Start smiling throughout the day.
(4) You asked:
"Another poster has told me to start acting like a man, and start being a leader - an alpha male, to use his terminology. In order to be that, I would need to become something I am not, and have never been. In fact, this would require me to change my personality entirely - to almost become someone else.
Is that what is required? Do I need to act like Dr. Jekyll, and find the potion that transforms me into Mr. Hyde?"
The short answer to your question is YES. If you are deeply unhappy with your life and marriage, then yes, be prepared to make massive changes. Your personality is not some hermetically sealed formula, nor is it set in stone. Its a product of all the experiences you have had so far, your mental reactions to them, and the beliefs you have as a result. Your personality, your values, and the image you show to your wife and the world, are all under YOUR control. No-one else's. Your personality is a product of your own willpower. If you really think that people are just "born" happy or strong or successful, you are wrong. Such people are in touch with their inner spirit and desires, and build everything else, including their personality, thoughts and actions, around it. Ask yourself what you current personality has brought you so far?
I will be back a little later.
S&A
"A man can be destroyed but not defeated" - from The Old Man and the Sea, by Ernest Hemingway.
Which I take to mean that every man has within him a spirit of relentlessness and optimism. Its already there; he just has to cultivate it.