I dont really agree with your partner .
We sometimes look for a reason for ourselves or those we love as to why we are how we are ....it makes it easier to cope with I suppose.
This is only my opinion , but its who brings you up that counts in my eyes , who is there for the upsets and the joys , and that can be one parent, bioligical or not.
If your mum or dad said it was your fault they split , or you wasn't wanted etc etc (like many horror stories I have heard) then I could understand you having problems over it.
Your mum sounds like a hard working determined woman btw