First of all you need to get out of this marriage pronto. Everything you've just said screams red flag. First of all, you've mentioned that she has children from another relationship. So basically you're using money that could go toward you and your children to take care of another man's issue. Think about that for a second.
Second, you're running a serious risk of being set up for paternity fraud:
http://www.netscape.com/viewstory/2007/02/18/30-percent-of-paternity-claims-are-false/?url=http%3A%2F%2Fwww.worldnetdaily.com%2Fnews%2Farticle.asp%3FARTICLE_ID%3D48871&frame=true
Check it out: false paternity hovers around 30 percent in marriages. Any child your wife has while you're married has a 1 in 3 chance of not being yours. Think about that for a minute: you could pay hundreds of thousands of dollars for a child that IS NOT YOURS. Oh wait, another child that isn't yours. If there was a casino where you stood a 1/3rd chance of losing everything you own would you would you even go? And as you've said her biological clock is already ticking, chances are she's more likely to try to use paternity fraud on you.
That's IF she isn't just trying to set you up for paternity payments. If you've lived with her for a year then in a lot of states that constitutes standard of living, and you have to pay to maintain that and for any kids she may have from any other relationship, EVEN IF THEY ARENT YOURS.
Divorce...you're equally screwed in that. Take a look at these numbers.
http://www.fathersforlife.org/fv/DV_news_letter_980130.htm
* 79.6% of custodial mothers receive a support award
* 29.9% of custodial fathers receive a support award.
* 46.9% of non-custodial mothers totally default on support.
* 26.9% of non-custodial fathers totally default on support.
* 20.0% of non-custodial mothers pay support at some level
* 61.0% of non-custodial fathers pay support at some level
* 66.2% of single custodial mothers work less than full time.
* 10.2% of single custodial fathers work less than full time.
* 7.0% of single custodial mothers work more than 44 hours weekly.
* 24.5% of single custodial fathers work more that 44 hours weekly.
* 46.2% of single custodial mothers receive public assistance.
* 20.8% of single custodial fathers receive public assistance.
Yeah, just in the act of getting divorced she has an advantage on you, which was probably her plan the whole time. How likely is this:
http://health.discovery.com/centers/loverelationships/articles/divorce.html
You stand at least a 50% chance of getting a divorce, even higher since you've both been in relationships before. And 2/3rds of the time the divorce is initiated by the woman.
Didn't you say your wife was acting crazy? Didn't you say she was unhappy? What do you think the chances are that your wife is either a) going to pop up with a bun in the oven one day and claim it's yours, or b) just up and decide she's going to cash out of your relationship now, get paid, and have a baby with another man?
My suggestion to you is to start speaking to male divorce lawyers who don't work for women. Get your assets covered and your affairs in order. You will be dealing with a divorce or an unexpected pregnancy in several months, believe that. Google "Men's Rights Activism", and look out for sites that protect men's rights and debunk feminist-socialist bullshit. You are in bad straits right now, but brothers are standing by ready to help.