Don't be the walk away spouse. (read up on this, lots of information about 'walk away spouse')
DON'T DO IT!
You have been married 15 years.
You just started a beautiful family
together. You stepped up your responsibility big time by bringing kids into your lives.
You love her and don't want to hurt her.
THEN JUST DON'T DO IT!
I read you feel smothered because your wife doesn't have any friends. What I hear is that she has placed such value in your companionship that she doesn't seek others. I did the same thing as your wife, and it made me very unhappy and lonely myself. I expected too much from her companionship and when she couldn't fulfill me completely I got resentful. I blamed myself for not trying hard enough, I smothered more, and I got more resentful.
I'll tell you something - I am not like that anymore because I no longer expect my Wife to MAKE ME HAPPY, or to BE MY EVERYTHING. I'm responsible for making me happy, and I choose to do it in such a way that it doesn't negatively affect my relationships. A lot of it is just attitude and outlook on life. My world doesn't revolve around one individual, her OR myself. I got here by accepting that, and I am an infinitely more happy person now because of it.
On the flip side of that coin, SHE had some of the same issues but not as severely. She had to stop ENABLING me to have these unreal expectations.
Like the other guy here said, how often to you watch the kids so she can go out? Also do you make it uncomfortable for her to go out, over any jealousy or other issues? Are you suffocating her without seeing it by wanting her to stay home?
After so long without being 'social' it may be hard for her to step back out again, it was for me! HELP your wife - talk about what she enjoys, there is a hobby around almost anything. Hell, get a sitter and go to something you think you may both like, go together and meet new people, meet old and young, singles and especially couples with healthy marriages. Maybe go to an event together and enter as 'strangers', have fun individually with others, and leave together. I guarantee you'll have something to talk about other than kids and the weather on the ride home!
Let me tell you something about intimacy. I have YET to meet a woman who doesn't CRAVE intimacy, I think it's how they're wired. SHE WANTS it and she WANTS it with you, or she'd be looking for it elsewhere. It can be incredibly hard to 'reconnect' after losing it, and new young ones in your life are a natural way to 'lose intimacy'. I can almost guarantee she wants it as bad if not worse, but YOU have to do the work to get it back.
My wife and I recently took a marriage enrichment course together, met some really great couples dedicated to their marraiges and had a great time. I want to talk to you about Dr. John Van Epp’s Relationship Attachment Model, something our course was built around. See the RAM board:
The rule is that in a healthy relationship, each bar to the LEFT has to be higher than the bar to the RIGHT. You have to Know someone before you can Trust them, you have to Trust them before you can Rely on them, you have to Rely on someone (know they're reliable) before you can Commit to them, and you have to Commit to someone before you can Touch (be intimate) with them.
It seems so simple but I believe without a doubt that it works. And you know how you Know someone? You communicate. Not talk, not listen, communicate.
Just do it, your family is worth it.
The other thing you said, I'm tired of being married? Lemme tell you something: get over it. GET OVER IT. You're bored, you think new and exciting would be good? Maybe you need to get a hobby too, take care of yourself. Your wife doesn't owe you excitement, and what she does, her commitment and love, it sounds like she's giving it to you.
Finally, don't think for a second that if you reject your wife, walk away from your vows, and test the waters for a while that things will get better. It is TRULY a last ditch measure only when all else has failed. Don't think that if you walk away, you won't be tempted to stay away. Don't think that the woman and family you walk away from will accept you back after you break the commitment and trust this badly.
Communicate with your wife, line up babysitters so you can go to a pro-marriage counselor, and take care of responsibilities so your wife can make friends and be the independant exciting woman you married in the first place. Things are going to get better, don't throw in the towel now because the finish line is right there.