With your child's tears at being with their Dad on his week, or rather being away from you?
Had my 9 yo crying on the phone (her phone not his - not a smart phone a Nokia)that she is lonely at her dad's. He tends to spend alot of energy on the 4 yo and not really be very emotionally available to her.
He's not abusive to her in any way, just not the same as Mum I guess.