Hi OldRedFox! Yes, here I am, raising my hand

(stepmom).
There are more stepparents on this site, mostly stepmoms. While my husband's kids don't have PDs (they are still teens), the kids' mom has many BPD traits (and she remarried to someone with strong NPD traits), so I get the challenges of being in a stepfamily with PDs in the mix.
I joined NAMI so as to get support

Good call. Whatever anyone else in your life is doing or not doing, if you need more support, that's good that you chose to get it.
My husband struggles with how to cope with his son's conduct
Where is your stepson (SS25) living now? Your place? Mom's house? Other?
I have thought about leaving my husband many times due to enabling and blame shifting.
PD dynamics wreak havoc on the relationships around them. Does your H recognize that the relationship between you and him has been rocky?
Are you both seeing a marriage counselor? If not, if it were framed as "improving our communication" or "I want to learn to listen to you better" or something NOT about SS25, do you think your H might attend?
I am exhausted and looking for others who have shared experiences.
Yes, I understand. This is a good place to share with others who will "get it" right away.
How have the last few days been?