The first thing to remember is that you are more than good enough person to be a grandmother. I suspect by saying this your SiL was hoping you would beg and weep and ask to please be allowed to see DGS. That way he would have had you under his control as well as your daughter.
By accepting his edict, however, grief-stricken, you have protected yourself and your daughter. Yes, your acceptance may be used as proof you do not care, but your daughter will know deep down that you do, but your distress and pleas cannot be used as a far more powerful way of manipulating her.
How do you cope? I do not know. I will leave that to the respondents who speak from the place you are in.
All I would say is that, hopefully, one day, your DD will break the spell, and return to you with her child and you will be able to welcome her and help her. Strong with the knowledge that having not compromised yourself by leaving yourself open to this man's manipulation you will better be able to help her
Hysteroscopy using spinal block/epidural
By special request, let’s discuss our favourite Classic Music and why?
. We have been estranged from our son for over 4 years now. Haven't seen our eldest GC since the age of 8 months, now aged 5, and have never seen our youngest of 14 months.