how am i supposed to feel

I want a baby so bad, me and my boyfriend just started trying because we both decided we want a child. while the 2 years of us being together I've watched his brother have 2 kids with a woman and he left her now he's with another woman and having another child. me and my boyfriend have been together longer and I just feel so jealous. everyday I hear about how she is pregnant and how she keeps forgetting that she is pregnant. like how do you forge? I also feel like she rubs it in my face because I have told her and his brother how we want a child of our own. but constantly hear about them and I don't know how to feel or even tell her I'm happy for her but stop running it in my face