Let him take his time. If he needs check how living with dad is like, just let him do this. i think the most important for you is to let him be happy. I know, maybe you are great mum, love the son much. But listen, he thinks that dad loves him as much as you. I don't know if is like this or not. Simply let him check by his own. If he still calls you and talks to you, it's nothing about your fault or that you are bad mum. I'm crossing my fingers to his coming back your home! For sure you are an amazing mum if you carry so much about living with your child. I'm sending you hugs!