Why would you feel guilty? I was in the same position as you still am but with no guilt.
My eldest 2 ds who incidently are severe SN, their ass wipe dad is not around wasn't from the youngest as a baby.
I don't know where he is, where his money is, can't track him nor do I care. I left very quickly for reasons I won't go in to. He does not even know his children are SN for example.
Both ds were young when I met my DH, he is their dad. He knew when he met me the score and when we moved in together, my career was grinding to a halt, due to needing to care, his was starting. Tough couple of years, then things got easier, we are now married and having our 4th child.
We have a comfortable life, he earns good money allowing me to be at home to care for ds', we do get some help towards costs but it's no where near enough his wages cover everything basically. I don't feel guilty we are soon to be a family of six, just because the bio dad was an ass not interested, nor would I want him to be tbh. DH took on the full works knowing what he got into.
And he is a stunner, I must have been good in a previous life 