I don't believe Joel is necessarily creepy, controlling, etc. and is rather just pretty annoying. I just don't think this level of emotional intensity is sustainable or healthy. Carrie was in a many year long relationship with Oliver and should be grieving the end of that and spending time with herself and putting her life back together. She's not doing any of those things.
My longest relationship was almost three years and after it ended I spent a full year grieving and going on one off dates and feeling lost and putting myself back together and briefly dating someone and ending that and changing jobs etc. And I still entered my current relationship with a fair few hang ups and things to still work through.
Her relationship with Joel is built on desperation to get back to being a member of a loved up, long term couple. I guarantee she slid into several people's DMs, he's just the one that stuck. Someone said in the last thread that rumor has it Panto was Carrie's backup plan if nothing else worked out for the fall/winter and isn't that really what Joel is too? A bid against emotional unemployment.
She is running away from whatever feelings she still has about Oliver and about their imagined future together.
I would say after things end with Joel all those repressed feelings will hit and she'll be grieving two relationships at once but let's be honest, she's probably going to marry Joel to avoid having to feel anything. Joel is not the love of her life, he is a stop gap against pain and I can't see their relationship being successful in the long term which is a pity because I think if she'd started dating him under different circumstances they'd be quite well suited for each other.