Of course we all want to be supportive of our friends and loved ones, but not if is taking an emotional and possibly physical toll on us.
If you are concerned about the effect the stress of this may have on you and your husband and your plans for a family, you have no choice, but to step away.
None of us have any control over anyone else. Has all of your support and listening and being there really made your friend's relationship with her A boyfriend any better? Doesn't sound like it.