I'm going to make some assumptions because not all of the backstory is here...
The main assumptions I am making-
1- Neither of you is a minor [I am assuming you are both 18 or older]
2- You are not attempting to marry.
As a practical matter you should immediately determine if you are related to this man on the basis of a half-sibling blood relation because that may very well impact a decision regarding the possibility of abortion.
The longer you delay, the more legal issues you may face if/when you attempt to procure an abortion.
On a personal matter, for my part, if this were my situation, I would immediately determine if there is an actual half-sibling relationship, and if there is such a relationship and it is documented and proven, I would strongly consider an abortion.
