It's painful because you want the closeness and have a gut-level fear that your therapist will withdraw/become distant just like your mom. At least that's how it was for me. What resolved it for me was the ongoing nature of my therapist never turning her back on me. No matter what stunts I pulled... no matter how much I 'tested' she stayed the same. It taught me how to successfully attach to people appropriately. For me.. it was what they call 'corrective experience'. It changed my life. But it takes time. And until you really believe that your therapist is not going to emotionally abandon you.. its going to be painful. You can't 'make' yourself believe it tho. It's a process that happens on its own. All you can do is walk through it until you 'get there.'. Trust me.. once you are on the other side of this... the journey will be worth it.