It seems you are maybe in the denial-shock/ anger-bargaining stages of grief.
Rather than go chasing the ex, consider learning more about the stages of grief
so you can monitor yourself and how you journey through them. You will feel all kinds
of things, and sometimes you ping pong through the stages. It's ok. You will make it.
Choose HEALTHY things for you. Not unhealthy ones. You are responsible for your own well being.
It is hard to feel, it will suck, but if you have to go through some short term suckage to end up at BETTER long term health it is worth it. Certainly worth more than being tied to a lying, less than stellar ex that disappoints you.
I mean that kindly, but firmly.
Could choose self respecting behavior for yourself even as you do your self care while you grieve what has been lost and what could have been.
You are at the place of WHAT IS here. Do not run from it. You are mourning and grieving. Could choose to be willing to do the work of grieving in a healthy way.
You may not be at the stage to move forward yet into the "acceptance and hope anew" place but don't go BACKWARD to the ex that disappoints. You are in Hang Time, like a time out. Be ok being in Hang Time -- let yourself process your grief. It can take some time to gather yourself back together.
How can forum people best support you in your grieving? You are not alone here. I see you, others see you.