> So because my mother cheated on him it's his fault for leaving
No, independently of your mother cheating on him, it's his fault for refusing to uphold his legal obligation to materially support his children.
Leaving the spouse is not the issue. (Leaving the children may be an issue, but to the extent it is it is at a minimum mitigated by fulfilling the legal support obligations a parent who is not raising their children has to those children.)
> If my father had cheated on my mother I'm assuming it would still be his fault if she left him
Whoever's fault leaving is, it would be his fault if he chose to refuse to meet his legal obligation to support his children.
> We grew up poor because my mother cheated, not because of my father leaving.
From your own description, the poverty was at least in large part because your father refused to pay legally-required child support after leaving you and your mother. Assuming that there was not a custody contest that you omitted in which your mother was awarded full custody, leaving children is not necessary with leaving their mother, however justified the latter is, and in any case, neither requires being a deadbeat on child support.
No, independently of your mother cheating on him, it's his fault for refusing to uphold his legal obligation to materially support his children.
Leaving the spouse is not the issue. (Leaving the children may be an issue, but to the extent it is it is at a minimum mitigated by fulfilling the legal support obligations a parent who is not raising their children has to those children.)
> If my father had cheated on my mother I'm assuming it would still be his fault if she left him
Whoever's fault leaving is, it would be his fault if he chose to refuse to meet his legal obligation to support his children.
> We grew up poor because my mother cheated, not because of my father leaving.
From your own description, the poverty was at least in large part because your father refused to pay legally-required child support after leaving you and your mother. Assuming that there was not a custody contest that you omitted in which your mother was awarded full custody, leaving children is not necessary with leaving their mother, however justified the latter is, and in any case, neither requires being a deadbeat on child support.