[processing please hold]

I'm sorry about your moms death. I don't have any male friends and my husband doesn't have any female friends. It works for us that way.

[TalonDJ]

Being more than casual friends with someone requires effort of some level. The more you have in common with someone the less real effort it takes. People put out effort to be friends for a reason. With family usually the common blood is enough that very little effort is required. With old friends common history makes the effort also very small. For males the only reason to expend that effort to be friends with a female is the potential. If the woman takes that away then there is no reason to expend that effort anymore.

Does all that sound kinda coldly analytical? It is but it is still true.