OP,
Kindly meant but you are a mug.
This loser and his children saw you coming.
Within 18 months he has you fulltime skivvy aupair for HIS children.
He does nothing.
Of course he has you pregnant to cement the arrangement.
What on earth were you thinking?
He's a lazy user loser and he's in YOUR house.
Don't make things worse and marry the loser.
Your life is going to be so much harder with a baby and instead of having a lovely time with YOUR baby, you will be skivvying for him and his children.
So sad.
There are so many threads where women bitterly regret your situation and within a few years are gone.
The lucky ones never married and just told the men that they and their children need to leave.
The unlucky ones married, and have all the complications of divorcing and possibly loosing their house.
Of course you being single and solvent with a career and home were of huge appeal to him.
Lazy losers love a woman with a home they can move into with their children and get her to be the skivvy aupair.
Don't marry him.
Keep your full-time job.
Keep your family and friends close.
Things with a new baby are so busy, but very very hard when you have allowed a loser to make a skivvy out of you in your own home.
God love you and your low self worth to have allowed this to happen.
Apologies if what I have written is harsh but you desperately need to wake up and see this situation clearly.