Nursery friend

My little boy has become really good friends with another little boy in his group at Nursey- pretty much inseparable when they are at Nursey, my little boy arrives after his friend does as they start at different times. He comes running over and their both always so happy to see one another. they’re always together when I collect him too- they both start and finish and different times so I’ve never had the chance to see his parents. My little one tends to start later and finish earlier. I found out today that his little friend has now left Nursey, do you think it would be okay for me to ask the nursery to pass over my number (I don’t know if he’s moved away- nursey just said he’s left, he’s gone to family) so I’m unsure of the situation. My little boy has been asking for his friend all week. (I know he’s only 3 and he’ll soon forget) Don’t know if I’d be over stepping the line by asking. I know if it was my little boy leaving I’d of wanted to pass over my details but again I’m unsure if the situation. Thanks x