Hi theliveingf, welcome. You are definitely in the right place for stepparent support -- when there's a PD dynamic in the family ,"normal" divorce/stepparenting groups don't always get it. It's next-level stuff so I'm glad you found us.
First of all,

for this:
I have also had emotional struggles and take medications for depression and anxiety, I worked very very hard to pull myself out of a suicidal hole.
Yes. You're not alone. Going through something similar right now, and it's very difficult to try to care for yourself when you're there, and then also try to stepparent the best you can. Really, really hard stuff. Support is critical so it's good you're here.
I'm also a stepmom; my husband and I have been married almost 9 years and together for >10. The kids are 16 & almost 14 now, so I get where you're coming from, it's the long haul.
While the kids don't have PD's per se, they often "import" conflict and toxicity from their mom's house (short story, she has strong BPD traits and remarried quickly to someone with strong NPD traits...yay...), and that creates its own type of stress, anxiety, and tension.
What you're going through is so relatable:
I often feel resentful of the attention she requires and the situations she puts everyone in. From cancelling vacations
We had to mentally prepare ourselves to take an overseas trip -- that we'd planned to do with the kids for over a year -- without them, if their mom manipulated them into "not wanting to go". While it worked out, that dynamic is so, so familiar.
I've also recently stopped commenting on anything related to the child with BPD, or trying to help.
I am moving that direction, too. It's too stressful for me to try to "help" with scheduling makeup time. I hate feeling like we're losing time with the kids, but one message you'll hear here over and over is -- we can't help others unless we take care of ourselves first. Please believe me that I am saying this to you while struggling with self-care myself. It's hard, and feels selfish. It's a process.
looking for other's who may be in a similar situation and hear how they handle situations and the day to day irritation.
Lots of stepmoms here so keep checking back in for more replies. Before we drill down into specific situations (it can be really helpful to "game out" some exact things that have happened or will probably happen), just want you to know that yes, things can get better. It may be hard, yet it is possible for things to be "less worse".
Hang in there and post back whenever works for you;
kells76