I'm concerned that you shouldn't brush it all off to hormones. It doesn't appear to me that she sees you as a full partner. I've both had a child and supported my gf through a pregnancy (and subsequent miscarriage) and I have to say, she always made me feel needed.
Besides, all this started before the hormones, right? Also, for me the passion is a real indicator. The fact that she can go WEEKS without being with you (despite sleeping side by side at night, I presume) and will have sex with her husband whenever he's home speaks volumes. It sounds like she's not that into you anymore. I hate to say it, but if she does get pregnant and have a baby, you will be even less of a priority for her. Unless you are an integral part of her support system from the get go, you will get pared down.
Please be careful with yourself. What does she say about the long term? Are you supposed to co-parent with them? If not, will you move out when the baby comes? What if they do move, will you then move but not live with them?