I have to say this is one of the best threads I've ever read here. And, of course, perfect for the Mature Man forum.
BB - I've been through a very similar situation and it definitely ended badly. Very badly. I truly hope that your situation is different, but I suspect that ultimately, it will not lead to eternal happiness.
AFC confession: After each breakup or announcement of an intention to breakup, the foremost emotion I remember feeling other than utter devastation, was REMORSE. I felt so fucking bad that I had been such an asshole. The truth was that this is a phony emotion that we channel our sorrow into because our first impulse is to blame ourselves after our anger and shock subsides. I suspect this has something to do with the stages of grief.
One observation: As has been mentioned already, when women break up/move out, they almost always have a replacement lined up. Keep in mind that this doesn't mean there is a guy she's been fucking behind your back, but it almost certainly means there is a guy she's been talking to.
Beyond that, you have the bitches coven of all her friends lining up behind her ready to pounce on you at a moment's notice. Judge by their reactions already: They can NEVER be trusted again and, it goes without saying, that your gf can never be trusted completely again either.
This whole episode is a gigantic breach of trust. I feel your pain and also your excitement at the renewed passion. You may remember that I've been divorced twice and went through similar things. I loved both of my wives and tried to save my relationships, but became a useless AFC in the process.
I hope this one turns out differently for you. I'll say again here that getting her pregnant right now is a HUGE mistake. Go ahead and fuck like bunnies for now, but until you at the very least have a hard sign of commitment from HER part, other than this silly thing of proposing and her accepting (what's her risk? what's her downside? --she holds all the cards!), don't even think about making a decision that will change your life forever and forever chain you to someone who has breached your trust in a very big way.
Until you have heard your child, your own flesh and blood who you watched being born in the hospital and who has your eyes, your ears your mouth, until you hear that child call another man, "Dad," then you have no fucking idea what it feels like to have a breakup with a woman who has your child and then moves on with another man.
Again, I'm pulling for you man, but this has the greatest chance of becoming your reality in the future.