hmmm...i have to think about this....men do NOT lose their sex drive in their 40's.
they may lose stamina or length of time....involved...but never the drive.
once every couple weeks?
there has to be something going on with him...my only guess is that it's a physical problem of some sort.
unless there's a silent type argument going on and he's witholding.
i can't think of a rational reason from going from hot and heavy to once/2 weeks in a 6 month time...have you tried asking him?