Options to help?

I've posted before about my boyfriend disappearing from me and our son, and ignoring me completely. Probably due to conflict his mum is causing (trying to cause issues in our relationship so we can't be together). He often goes off for a few days when struggling but this time it had reached 4 weeks.

He works with my family and the other day my mum approached him when he was alone and confronted him (in a nice way). She asked if he wants to see our son but is struggling to contact me as he has left it so long he doesnt know how to approach me. He said that was right. She offered to arrange for me to bring our son over that day for him to see and he was really happy. She asked if he would prefer me to just drop our son off or if he wanted to stay too. He said I should come. I acted completely normal, didnt mention anything that's gone on. But he was so different with me, didnt make eye contact, put his head down and stopped talking much when I was near by and he didnt talk to me. When he left I just nicely said he could message me any time he wanted to see our son and he said he would do.

That evening he messaged my mum saying thank you, he needed the push as he never knows how to resolves something or make the first step. She replied offering to arrange more visits with our son and he told her he was fine to message me now the awkward bit was over. He then opened my unread messages the next day (which were only brief updates on our son). A few more days passed so I sent a short message saying "hi hope you're well. Let me know any time you would like to see ***". But he hasn't even read it.

So. I am thinking, do I just approach him like my mum did. As he said to her he needed the push and cant make the first step. I could wait until he is alone and just try to talk in a nice calm voice and being careful not to upset him or let on how upset I am. Or will that likely push him further away? Maybe he wont handle me approaching him as he cares about me whereas he doesnt so much with my mum? 

The other option is, I could approach his mum and try to resolve the conflict by showing her the affect this has on her son. Then we can maybe let him know things are fine between us and the conflict is resolved. But I would have to show her his messages to me where he opened up about his mum. Which would upset her and I've shown confidential messages he sent me. So would he then hate me for it?

I know no one has the answers or a definite solution. But I cant sit and do nothing anymore, it's making me ill worrying and missing him etc. But without fully understanding an aspies mind I dont want to do anything that could make things worse. Thank you