Absent parents

Allysia

So my 5 year olds mom hasnt been in the picture for almost a year due to drug use. Before she quit taking him we did 2 weeks on 2 weeks off.we tell him that his mom is sick and not making good choices so she shows him she loves him by staying away. We do have him in therapy which seems to help a little but not a whole lot. But lately he seems to be really angry with us and thinks that were keeping him from his mom, when we try to explain that its mot our choice but it is hers he gets really angry and says no it's not. So I was wondering if anyone knew of a different way to explain to him that its her choice and not me and his dad trying to keep him from her.