Help! I'm jealous!

I know jealousy is a horror trait but I just can't help it in thus situation. My partner and I have been ttc for 17 months with no second pink line ever. He got his ex pregnant (it was a surprise) very quickly. I am jealous he has had this experience with someone else. I'm annoyed he forever has a connection to this other woman. Don't get me wrong, I treat his son with all the love and respect I can.. but I feel like our time won't be as special now because it has already happened with another person. I feel awful for feeling this way!