If as I understand it, you are still in touch with your grand son's father, who hopefully understands the situation, you will presumable also know his parents (the other set of grand parents) ...how well did you get on with them, and could you share your feelings with them ....they may also want to see the grandson ...and if so, perhaps you could spend time with him at their house ?
I found out where my daughter is now living, and with whom, from the internet ....there is also a child shown in the photos online ...although I have no idea if this is my grandchild or a child of the new partner (D not spoken to me for ten years, so it is possible the child, who looks about 8, could be hers ...just do not know !) ...however, decided it is her life, and if that is how she chooses to be, then there is nothing I can do about it ......it took a long time to make that decision and I admit to still sending her cards on her birthday and at Christmas (since finding her new address after about a year !) .....my step daughter tells me I am stalking her and she could complain to the police ......yes, good, I will then maybe find out why, and be able to put my point of view !
Very sorry to hear of your situation ....I hope it is temporary ...what do you know about the new BF ..he sounds a bit controlling ....I believe there is somewhere now you can check a person's background ?? or you could always hire a private detective to find out their address (I did this once, no animosity involved, to find my husband's brother after their mother died ....quite reasonably priced, and a very quick solution ...they are now in touch again after about 50 years !)