You don’t have to be married to co-parent together

Really depends on how much they like each other.

They should get married if they love each other

Yes, he should be responsible for his actions.

It also depends on the relationship actually

Yes, if he doesn't love her, why have sex?

Depends on what both of them want together

If they want to spend their life together

If it’s mutual understand then only yes

Depending on the choices of both parties