About turning 30 and feeling the clock ticking, far be it from me to sympathise with Carrie, but I think Tom being so settled makes it harder for her. Especially if people in her family (I don't mean directly her parents, could be other members) are hinting that it is about time for her to settle as well.
At least I know I'm fine with not having kids or being married in my early 30s, but when someone from my family makes some remark about my cousins being well ahead of me (I got no siblings so cousins are the closest) it hurts and it makes me a bit anxious. Then I luckily get over that pressure.
If anything like that happens to her, it must hurt even worse coming out of a long relationship that failed, since it nearly feels like you somehow threw away years of your life. Not saying it's right, but it can feel like that sometimes.