The strained reunion I have with my son is torturous. Can anyone else understand how I feel?

I gave up my son in an open adoption back in 1984. We’ve had a strained relationship over the years. He got married a few years ago, and in May 2012 he and his wife had a baby boy. I have never met my grandchild; my son didn’t even let me know they were expecting. The only contact I’ve had with my grandson is by seeing Facebook photos. I’m heartbroken. No one that I’ve talked to or read about seems to relate to my situation. I feel like I’ve given up my son all over again. It’s torturous. Is there anyone out there who has faced this and who can understand how I feel?