Need some support/advice

So my boyfriend has a child with his ex, and she is pregnant again (hasn't been with the father for long either) and I feel weird? Like the way you feel when you are nervous? I'm sure its not jealousy? How can I cope with this? It won't effect me in any way, I work with children so helping his child with the transition won't be an issue! Ahh what am I feeling and why?