Confusing emotions

So my husband has a 12 year old son who lives in another state with his mother. we see him random weekends and about a month out of the summer. My hubby was never in a relationship with her but they still share a child together.

We have been married a year and half and are talking about starting a family of our own and TTC in the next few months. I hate that I feel this way but it is difficult for me to know that I am not the one who can make him a father and give him his first child. I know I'm probably being overlysensitive but for some reason it gets to me.