What do you say to your 7 year old grandson?

What do I say? What words does one use? I have been deeply involved in my grandson's life from the day he was born. We've taken trips together. He loves it in my home and never wants to leave. However, the relationship between my son and daughter-in-law and me, has become toxic and there is nothing that remains. I have delved deeply and simply cannot find the answers on my own. My son refuses to answer regardless of how much I plead. I can no longer be involved in the lives of my 7 year old grandson or my 3 year old granddaughter. How do I tell him that I always have and always will love him and how much joy he has brought to my life? I know him and I know that he will sneak and call me. He has done it in the past. How do I not hurt this precious child? Please... no rude answers. Thank you.