BM's boyfriend---a question

[jojobear]

My ex has filed for custody of my 2 boys.  For 5 years they have lived with me and for 4 years they have had a home with my new wife and her 3 children.  We have all blended very well.  My ex is now trying to get custody.  My question is this.....My sons BM boyfriend (which she has a son by) is living with her.  He has 2 children that he is denied visitation with in another state.  He pays child support but is not allowed to see the children.  Should I investate the reasonings...since he is cohabitating with my children every other weekend?  And if so, how would I go about researching what the factors was in his supervised visits?  I have wondered about from the start..but never cause to be alarmed from what my boys have told me....but now that the custody hearing is approaching..i wonder if this is an avenue I should research.