Whether the partner knew about the pregnancy: my guess is that it might have been complicated and he has plausible deniability.
For example: say contraception fails and a male partner asks their girlfriend when they would get emergency contraception. A girlfriend with a child already might reasonably say, I don't want to put hormones into my body; it made me sick before; we seem to get getting on well and I don't want a very large gap between my children in any case... triggering a row where the male partner reveals their hand, that they don't see this as a permanent relationship, and the relationship ends.
In that situation, we might well see a guy immediately going onto Bumble and crossing their fingers. And having had a fright, they become more determined at finding the right person, regardless of whether they will be right for the women out there if they suddenly discover a surprise child down the line.
Then whoops, 8-9 months later, he has to pull his head out of the sand. And while he can truthfully say he didn't know, he did know it might be possible - hence the frantic quest for the ideal partner, the girl who 'isn't like other girls', overwhelming them with 8 hours on a first chat.
It's sad, but the OP will clearly make her own choice and is probably in the honeymoon stage where she just can't be rational.
It's the little assumptions that need mythbusting, like any assumption that he will somehow make it up to her. But he can't. He has less to offer now. Her needs now come third - below the child, and below himself and his commitment to his job, which he needs to double-down on so he can provide and be a good parent. Time, attention and money don't magically expand in line with guilt. He will be dancing between more spinning plates, and sometimes they will crash, and OP will find she has to look out for herself - and how could she have expected otherwise?
Priorities will have to change promptly to put the welfare of the child first - the right thing to do - which will leave little time or space to come to terms with the situation.
The former girlfriend has something her partner wants - his child - and would be foolish not to negotiate the best possible deal with him, whether in terms of him providing help and support, or money, or both.
The OP may also find her partner playing a mental health card - she is the only one who can get him through this, he can't live without her, it would be unfair and cruel for her to ruin his life when it isn't his fault, he doesn't know what he will do...