Here's a background story to our marriage and our family (it plays a large role)...
We got married and had our first child when we were 23. We then had our 2nd child when we were 26. We are currently 30 years old and we still have only these two children. Something worth noting is that my wife never completed her college degree (assume that she hadn't done much or any of it, and it'd be a full credit workload from start to finish. Nothing carries over), and this has been a very significant goal and dream of hers since day 1 of me knowing her. And rightfully so, it's something I completely understand and have embraced as this will happen... eventually. In the beginning of our relationship, the money just wasn't there to send her to school. And then very shortly after, babies have been a show-stopper for her going to school (she is a stay-at-home mother).
Fast-forward to today, and our oldest child is now in school and our youngest will be going to school in 2017.
What I see
As the husband of my wife, I finally see us nearing the time for her to go back to school. We have money, and our youngest is going to be going to school full time starting next calendar year.
What she sees
... she wants to have a third child.
First off, this scares me. When I say that her going back to school asap has been a very significant thing, I mean very important. Not just a nice-to-do, but moreso a requirement. Let's say we get pregnant today, before the future 3rd child went off to school my wife would be 36 years old. It's one thing to have to wait 7 years, but it's another thing to have to wait a total of 13 years. Not to mention the additional financial burden of another child, realistically speaking.
Her response is that she is ok now with waiting that extra duration so that we can have another child. I believe she feels that way now (and has for the past year) but I don't see that as a lasting feeling when we are 33/34 and there is a 2 year old running around with another 3 years before he/she goes off to school. Her college degree has been that significant in our plans that it doesn't make sense to me.
Then there's another thing... I don't particularly want a 3rd child. I love my children more than anything in the world, but the truth is that they are a lot of work and I dont' have that same burning desire to have a 3rd child. It's just me, and it's how I feel. A little backstory, when we were first dating and newly wed we had plans of having 3+ children. My wife sometimes likes to remind me of that, but my response is always a resounding "things change" montra. It's easy to say you want 10 kids when you have none. You simply don't know what it's like. I am also a car person, and I used to want 3 old Chevies (a '57, an old '40s truck, and a '67 Chevelle). I currently own and turn wrenches on an old car. I love that car more than anything, but there's no way I want to have 2 more in the garage. When I was a kid, the thought of having 3 old cars was nice but there were many factors that weren't considered (not to mention just the changing tide of human desires). I'm using the car thing as an analogy, but I think it's as good reflection on desires-past to desires-present.
I feel like I'm at a fork in the road with my marriage over this. On one side, I'm having to try to decipher the future of her desires with an additional child vs. going back to school (sooner than later). And I'm also wrestling with my inclination/desire to not have a 3rd child. Don't get me wrong, my 2 children are the absolutely heart and soul of my happiness and life. They are everything to me. And I'd be doing a disservice to this question if I didn't say that, if my wife told me she was pregnant tomorrow I would have a fatherly instinct to be happy and excited about it. But that is different then actively trying to have another child.
These are things that, in my very limited experience, can break up a marriage. Maybe I'm just overly fearful, but things like not fulfilling desires of having more children or going to get a college degree can be detrimental.
I truly don't know what to do here, and I would greatly appreciate any advice you may have.
EDIT
This is a great example of a similar situation. It is worth noting that my wife absolutely sees herself as a stay-at-home mother. I don't doubt that the fear of our youngest going off to school has her doubting her busy-ness throughout the day. For what it is worth, I never pushed her to anything. I tell her that she is fortunate enough (given my single income) to be able to do whatever she wants, whether it is making money with a career, volunteering daily, or anything else. I tell her that when the kids are in school, that time is a blank canvas for her to paint any which way (school, work, volunteering, hobbies, etc.).
Another thing worth mentioning, my wife is relatively hard-headed (aren't we all?). She gets desires and they aren't easily transferred. Even with my objective output, she still falls back on "this is my internal drive". And she also has the fear of being a 38 year old woman still wanting another child and then biology starts to play a role.