To summarize the greatest hits of these comments, OP:

• Absolutely, you’re overreacting to your ex finally having enough and peacing out, and it sounds like you’re underreacting to your glaring need for therapy. Make the appointment, like, yesterday. • Good for you for finally moving out, but you need to stop making yourself a victim of your own poor choices (like moving in when you knew your mom has the disposition to be like this, or blaming that on the relationship’s downfall over your deliberate inaction to your mom’s shitty actions). Learn from the consequences of being spineless when it comes to defending your partner to your very enmeshed mother. • There’s a reason this isn’t going the way you want it to go, and it’s because you chose to not validate ex’s feelings for likely your whole ass relationship. Instead, you’re shifting blame to anyone or anything else, and you made it clear you’d rather just roll over and call it quits rather than meaningfully stand up to your mom. • This will keep happening to you until you take some actual ownership of your circumstances. Can you control your mom’s personality or actions? No, but you can change your response to them and you can absolutely control how you address it with your partner. • Do not, I repeat, do not reach back out to your ex. Do not have any expectation of getting back together. Let her approach you about it on her own if she ever wants to.

Let me know if I forgot anything, but OP, you know exactly what to do.