Step Parent I know my place

Being a step parent is hard however I know my place ! I am 23 no kids of my own! The man I wanted to be with has 3 kids with his previous relationship , me being in love I thought nothing of it almost 2 years later down the road and still have not gotten use to things. I find myself thinking in selfish ways and at the end, end up feeling bad because the kids run through my head constantly. Coming from divorced parents I know the first hand how it feels to be a child and your parents seemingly moving on with there life’s I get it ! I know my place however I overwhelm myself  with thoughts like what am I really ? They know who there mom is however I do everything take them to school bath them homework dinner awards concert etc while she is just living her new life with her new family! Kids don’t know the reality and they shouldn’t at the end that’s there mother and they only know what we show them and I would not want to influence them wrongly about there mother! But what is really my place I’m I just a person on the side like a maid to serve and make everyone feel something when I can’t even take care of my own self and I’m just trying to do what’s right and how I would have liked my step parent to have treated me. But then when I over step example educating the boys the right way how to clean and have manners and get talked down with things like I don’t like how you talk to my kids and not get offended ? Over stepping never again however do I give up that easily ?