Op, it’s harsh when is being said to you but at the same time, I think you need to hear it.
You’re using an open forum to be brutally honest about your feelings to two boys who by the sounds of it, have already had a rough start. Your feelings like to a counsellor wouldn’t reveal so much honesty that other posters have put here.
I lived with a step parent from the age of 6. They couldn’t have been any better of a parent to me, and are now classed as my DF (I rarely describe him as DSD). So what did he do that you could do?
Age 6-11: he played with me, provided for me, loved my mum unconditionally and us as part of the package, showed me love and kindness, cuddled me when I was scared or sad, made me laugh so hard all the time; encouraged a relationship with actual DF; was disappointed when I made mistakes but encouraged me and love me despite them.
Age 12-20: he looked out for my education, provided advice based on his own mistakes and experiences, he had my back with anything (boys!) that made me sad or pissed off, never talked badly of actual DF, organised birthday parties / events, was my Taxi to / from work and to where I wanted to go, picked me up at 3am outside a nightclub!
I know I’m writing really obvious things down, but perhaps you need to see what being a parent is since you’re still in this “loved up” stage of parenting where everything is babies giggling and being cute.
Parenting is fucking hard but being a step parent takes that little extra effort. My DSd never tried to be my dad. But his love for me was from day 1 when he entered my DM’s life. He became our family because of how he behaved towards me and my DSis
I hope you work this out.