just be honest. as soon as possible tell him..personally.
arrange for someone to leave the kid in a basket on the doorstep just before you get home
Invite him over to and have them meet. You may find out he likes kids. If not then you know the next step.
Yikes! That should have been known from the beginning. That's not something you hide or wait for a later date to tell. First and foremost you are a mother....so now you run the chance of him leaving. Having a child is a big big deal....so just be honest. Maybe it will work if this guy thinks being a dad is a possibility.
When you are out with him, just tell him"excuse me,i just want to call up and see if my child is ok".
Before we even got serious.