From very early on in our relationship, my husband knew that I felt children were a 'must'. I had worked in daycare, and was a preschool teacher, and I babysat when I was younger, and volunteered at a local sports club in my youth to be assistant coach for various sports. When my husband and decided to explore 'family planning' I spoke to my doctor about (what at the time seemed like) a small issue I had dealt with for years, I very quickly found out that conceiving was not going to be an easy feat for me. I was given all my options, and assured that pregnancy was not off the table without first trying IUI (and IVF), but I was bitter as hell.
I have two siblings who are much older than me, so my relationship with niece #1 and nephews from them was not affected at all. However around the time I learned about my fertility issue, my husbands brother and his fianc had 'accidentally' conceived. Having their brand new baby (niece #2) around and knowing what trouble I would have to concieve in the future - was horrible for me at first. They had originally said they never wanted children, so watching them coo and fuss over their new bundle of joy brought out envy of which I had never felt. I'd never not wanted to hold a baby before. I'd never not wanted to spoil a niece/nephew. It took a year, and a lot of soul searching, for me to finally get my act together.
It's been three years since I 'found out' and I think being open and honest with someone about how you are feeling (whatever feelings may arise!) will definitely help. I didn't have that luxury, because none knew. I was so ashamed, I forbid my husband to even talk about it for the longest time. A few people know now, and I speak very candidly with my husband about my feelings and jealousies as all of our siblings start to make families and I'm still waiting. It truly helps to be able to be so honest with him, and for him to listen and understand and be just as honest right back to me.