My son is really scared of been alone, and it seems to get worse and worse. He's almost 4. Sometimes all I do is step into another room to trigger an emotional breakdown from him. I just can't figure it out. I stayed home the first 2 years of his life, breastfed past 2 years, and I'm currently working from home (part-time). He has a little sister who's almost 1, and he absolutely adores her (no jealousy issues as far as I can tell). He watches at most 1 episode of Thomas or Diego.
We talk about how powerful God is and how much God loves him and watches over him. We pray together for God to give him courage. But he still wakes up wailing when he can't find us. What can be causing this?