Sigh to the spam message above -- reported.
OP, I can see why you want your child to have a father. And to be honest, I don't think it will be easy for your exDH to get a visa to come to the UK as the parent of a British child (he's meant to show active involvement in the child's life, which it will be hard to do if he's in Algeria).
But as others are saying, he does not sound like someone who cares about being a committed father. You are heavily pregnant with his child, and when he cheated on you, he expressed no remorse. When you told him you wanted to split up, he said 'that's fine' 
... but told you he still wants a visa!
That's a terrible way to treat the mother of his soon-to-be child. If he treats you so badly, what kind of father is he going to be? It's the best interests of the child that matter here, and he doesn't seem concerned at all about the best interests of his child. 
Applying for a spousal visa under false pretences would be wrong. You are going through a terrible time, but hard as it is, how he gets a visa to be with his child now that he has treated her mother so appallingly is HIS problem, not yours.
You are young and the odds are strong that you will find a partner in the future who will be a REAL father to your DD.
