Baggage

My boyfriend I've been living with for 6 months just told me the other day that this girl he used to sleep with aborted his baby like 7 years ago. The idea that he could have a 7 year old with some girl named Chantelle makes me sick to my stomach. I feel like he's been closer to another girl than me or something. I'm prochoice but it sucks that he was so irresponsible with some random girl. Any advice on how to get over this or anyone who's experienced the same thing in their relationship??