Welcome Jmoet
Take a deep breath and don't act too irrationally. Little boys do masterbate. Often times it is more associates with self soothing than with sexual desire.
Being abnormally attached to your mother is identified in young boys that is why there is a name for the complex. It is not a disorder and managing both the masterbation and the attachment is what will resolve the matter in a healthy manner.
I agree with BBU that seeking professional help for you and your husband to learn how to manage this behaviour in a healthy manner is very important.
Your managment of the issue so far is what I would also have done. A simple explaination of privacy and boundaries.
My son used to cry out at night "why am I the only one who has to sleep alone!" We had a hard time keeping him in his own bed. So we established a rule that he could have snuggle time with us in the morning before we all got up. That resolved the issue. As he got bigger around 7/8 he said "I am happy I don't have to share my bed! There not enough room for all of us!!" He declared he only wanted to sleep with me. We kept explaining the role of child and the role of parent and this demand soon faded.
Best of luck. with the situation.
