I don't have as much difficulty with "promise" as with putting too much weight on what is said. Everyone breaks promises if what is promised is interpreted differently by the one making it and the one the promise is being made to. Promises can be "legal" and those I would consider bad to break but emotional promises like, "I'll never leave you" feel good but that's about all they're good for? Everyone dies so everyone will leave.

"I'll never abandon you" is something I would immediately put qualifiers on if it were to be said to me. I would add, ". . .while we are working together". As a statement made between therapist and client, both people are individual adults so the meaning is unclear as both individuals are always responsible to themselves. Even insofar as one adult could conceivably abandon another, who gets to define the meaning of "abandon"? If I love you and am emotionally attached to you my perception is going to be unbalanced when it comes to whether you have abandoned me or not and why. Anger is one of the emotions one has to go through in grieving for a loved one because the loved one died and left one living. But I don't think anyone will "fault" the dying person for dying?

The answer isn't to not become attached to people, not to ever love because eventually we always, 100% lose those we love, but to become an individual who can support one's self and work through grief to recoup the parts of self we invested in the other so we will have them to invest again. Loving and growing hurts! But the alternative is death.