read the posts here starting back a few years and you will see a pattern.  IOW its not you "going crazy"  StepMOM life is very much NOT worth it.  

In saying that I think my DH tries, in his own way, but will always have the instinct to believe their bio has "changed" or is just being a kid, or doen't mean it. Or (my favourite) it just me refusing to see the good. 

I don't think most BD's have the ability to see from an unblinkered view how their bio/s have tarnished their marriage, their spouses peace, happiness and life. It's like our experiences simply haven't occurred, or we are making too big a deal of them. In reality, for most of us we make far to little deal of it until it becomes absolutely untenable. Then the BD's feel they being made to "choose", instead of just stepping up and being a parent to their kid. 

I've had the "that's exactly what I needed" moment, because even if there has been some kind of mild consequence or play at empathy, it has only ever come too little too late, and after far to many fights where the skid has been excused for any and all atrocious behaviours (in laws too for that matter). After all the time trying to defend yourself against people who have been the problem that you get to the point where you know that you are seen as the issue, not them and it's just a way for the DH to get some peace without actually having to do anything.

I truly hope you have a very different experience.

My husband realized my pic better when he saw how I interact with my dad. I send him things to just make him happy, I choose thoughtful gifts, we have genuine conversations and he respects me for business advice. 

Meanwhile SD12 treats him just how his sisters treat his father. They act coy and sweet but really it's just buttering him up to get him to buy or do things for them. He always thought that's just how dads and daughters are.

I successfully launched and got independent and built a good career. His father is still paying for his sisters, one just pops out kids and the one is still partying like a college student even though she's almost 30.

He's told me he hopes SD turns out liek me but he's afraid she will be like BM, who is quite similar to his sisters in how she makes men (her dad or current SO's-plural because she usually had more than one at a time). 

Does my SO ever try seeing things from my side? Sometimes. He occasionally takes his rose colored glasses off and it's refreshing.

Are there ever moments in step-life when, "Wow! This is exactly what I needed!" can come out of my mouth? Yes! Every two to three months when the BM picks up her daughter and I get a nice, calm, peaceful, happy little break for a week or two.