Any man in a committed relationship that is still perusing online dating sites is doing something wrong. You have every right to be concerned, and I think you should talk to him about it.
I would ask him about whether or not his parents and family like you. Have they been telling him that they don't like him dating someone outside of the Jewish faith? Ask him about what he thinks. Does he see a future with you? It's not like you have to pry an engagement ring out of his hand, but you should try and get a sense of his thoughts. It's entirely up to you whether or not to bring up the fact that he's still on Jdate, but definitely try to talk about your underlying concerns.
Best of luck.
Ladies, have you been involved in some interfaith dating drama? How did you handle it?