You should encourage and support her to keep that pregnancy and make sure the child is raised responsibly. A responsible man takes responsibility for his actions and that pregnancy is your responsibility. How do you go terming her as irresponsible? It is interesting how you realise this only now after sleeping with her severally. But first wait for the birth of the child then you can do a DNA test to confirm paternity then if it turns out positive you can do what will be required of you. You better inform your wife and your parents of this pregnant lady and be ready to support her and her baby because it has happened after your prolonged relationship.

People already know of the story so in case she procures abortion and she dies or something happens you shall be the first culprit. I would not encourage you to ask anyone to terminate a pregnancy.