Your own life is your life. You live for yourself, selfish as that may sound, but that is how it is, and you are not defined though someone else. I find that important to point out.
But I am sure you hurt far too much these days, considering how very raw your wound still is, to really see this. Per part you may have begun to define yourself through your relationship with Michelle and her children and you have very happily taken up the role as partner and (step-)father. Which is good and shows me that you are strong and mature and willing to take responsibilities.
Things are turning a wrong way now. Something has been going on underneath the surface that is now erupting. You are being blamed (which, by the way, often comes out of the defensive of the other...) ... but show that same strength, maturity and responsibility towards yourself now, too. You are who you are. And you have all these strengthes. They are inside you. They are hidden underneath that landslide of shock, grief, hurt, disappointment, and I understand that perfectly. But they are still there.
It will be work.
But give yourself the time and chance to dig all your strengths out again.
You will walk through a deep and dark hollow for quite some time to come.
You will be hurt again.
And again.
But go that path and you will find out (you will!) that you come out stronger on the other end. Give it the time it needs, though, for you to walk through that hollow. You are hurting and grieving the lost relationship to three persons. Allow for your feelings. Come here and cry.
But never lose hope in your strengths and abilities, right?