Your emotions aren't unfortunate. I'm wondering why you need to characterize them in that negative way? You were in a relationship and it ran its course for you.

So many men end up hurting themselves and the woman they're with, staying with the woman they no longer love. Their resentment grows, they have affairs, they abuse the woman (or do worse).

The smartest decision that you can make, that will have a beneficial outcome for you, her and your baby together, is to break up with her. Neither of you are the "right" partner for each other, in your opinion. And that's perfectly fine. The worst decision that you can make it to mislead her into thinking you do love her, by staying in this relationship through her pregnancy.

Think about this rationally. You didn't like it when her thyroid disease caused her hormones to fluctuate since it made her emotionally unstable. She's pregnant now, so imagine how unstable her thyroid and hormones are NOW that her body is creating a human life inside it. She is NOT going to be rational. She is NOT going to be dependable. She is pregnant. Pregnant women's bodies endocrine and nervous systems hormones fluctuate and become "taxed" by the human life it's building. Your baby's development and well-being is determined by your girlfriend's body's ability to sustain life inside it. That means: weird food cravings, a LOT of emotional instability (due to her fluctuating hormones), fatigue, nausea, vomiting, etc.

So, I do not think you should stay with her, unless you are willing to set aside your jealousy of her ex partners, and be willing to sacrifice some of your social life to physically be at her beck and call, when she needs you to run to the shops for her, or take her to all the doctors appointments.

If you aren't up for doing that for 9 months, then you really should break up with her now because I guarantee that she will expect you to continue to be there for her after the birth of your baby and beyond and she will still be in hormonal imbalance after the birth for up to a year.

This isn't something to take lightly by any means. So, you really need to think about the ramifications of your choices concerning your pregnant girlfriend. If you breakup with her now, she'll resent you but it's for the best and if you have a therapist together to help you two transition, then you are better off than waiting until after she gives birth, b/c she'll think of your abandonment in far harsher light after the birth than before the birth of the baby. But that is my subjective opinion of course.

This requires a seriously transparent discussion with your girlfriend that you can't be afraid to have, especially since you're going to become a father. These types of discussions require a level of emotional intelligence that shows you are mature enough to rationally discuss this without it devolving into a screaming match or physical altercation. Does that make sense?