It doesn't make sense. It's the writers flailing. The 5 year separation was a ridiculous idea to begin with. Aiden and his family are boring. The only thing that made Aiden interesting in the first place was the fact that Big was always looming in the background of their relationship, and for a time, Carrie wanted him as the anti-Big. Without that tension, he's just a bore who Carrie wouldn't look at twice.
She only ever really wanted him when she couldn't have him. She cheated on him with Big at the first opportunity. When he didn't want her back the second time, she claimed she had never stopped thinking about him (total BS, the only man she obsessed over was Big) and demanded he take her back. As soon as he wanted to marry her, she started rejecting him. She didn't seem at all upset over the break up, more upset about being potentially homeless. She obsessed over him not liking her 2nd post break up ( the Nina Katz episode), but she cared more about what people thought of her than of Aiden's actual feelings. When she bumped into him with his baby, and they said they should go for coffee, she walked away pretty much saying she'd never see him again - no feelings there, she really wasn't interested in him. And that was only a year after breaking up with him.
She had a dalliance with him in Abu Dhabi because she was in a bad place with Big, nothing more, but it's Big she ran back to. She only wanted him post Big's death as a comfort blanket, but the messy reality of his life is not something she wants. She's got an idea of what her life might have looked like had she stayed with him originally, and she's probably breathing a sigh of relief that she didn't. His cheating with Kathy has given her the exact excuse she needs to back away with no blood on her hands this time. And to put an end to an unsustainable plot line. Let's hope that's the end of it.