I am also a 19-year-old woman in a relationship with a 38-year-old man. This may be surprising, but we do have a lot in common. We have a similar career path (although, admittedly, he has accomplished much more), we’re both very left-brain and have long conversations about math and scientific theory, and we’re both very athletic and work out together nearly every day. Although it is probably not common, there is a such thing as a healthy relationship with a significant age discrepancy.
That said, the fact that this man is the father of your ex tells me that this is not one of them. My partner does not have children, and I believe that if he did have kids my age it would be very awkward and make the relationship much more questionable.
My two cents would be to terminate the relationship ASAP, however I know from experience that it is nearly impossible to stop being attracted to someone.