Broodywoodsgal....your post totally made me tear up! (damn pregnancy hormones! lol) this is also my third, altho my partner's first and I find that it is such a mix of emotions this time around. My older two are now 7 and almost 5 and I feel like this time around I have such a different appreciation of how amazing/terrifying/exciting/precious/and everything else this time is. In some ways I think "I know just how overwhelming/stressful/life changing this whole thing is going to be...what am i thinking doing this again?!" but then i look at my boys and see that "I totally love you the best in the whole world, don't worry" look that you mentioned and I know that every moment of stress, worry, hardship, change is 1,000% worth it. You get through the tough times, you always do, no matter how tough they are (and with the situation with my ex, there were MANY VERY tough times).
So, OP, yes your whole life is about to change, every aspect of it, but that's what life is, isn't it? it's all about change, growth and evolution. Sure I miss the days where I could party till 4 am, or do things on a whim, or not have another human being entirely dependent upon me. But would I change it for anything in world? Absolutely not.
I was at the grocery store the other day and the cashier said "oh hunny, it looks like you're going to have to learn a little patience with a little one on the way" I smiled and said "I have plenty of patience, thank you. this is my third" Her response was "You don't look old enough to have three kids" people will be insensitive, people will make rude comments, people will try and scare you and say dumb things. for some reason in our culture people think it is their right or their duty. but at the end of the day, you will always have what it takes, even when you don't feel like you do. and the love a child has for his or her mother will always overshadow even the most negative of comments. i think that the feeling of being overwhelmed in the third trimester is nature's way of preparing us to have our hearts ripped open so that it can grow enough to love a child we have created. i so often look at my partner and think "you have no idea what you are in store for. you have no idea how much you are going to love our daughter" because there is nothing, absolutely nothing in the world, like that moment you first lay eyes on your child. enjoy the ride mama!