Second Wives - does it ever get better?

My husband was married one other time before we met, and they share children together. My husband and I do not have any kids between us, but we share custody with the kids from his first marriage and their mother/his first wife. He and his first wife had a very tumultuous marriage and a really angry and frustrating divorce (on both their sides), and overall, it gave him a lot of trauma and emotional hang-ups when it comes to relationships, communication, and marriage. He's grown a lot over the years, and acknowledges he still has pain he has to let go of, but I can still feel how his past experiences shape his response or behavior in our marriage today. It almost feels like theres this whole other person in our marriage at all times - like an elephant in the room. I try to be supportive of him, and I encourage him to still stay friendly with his first wife for the kids. We all speak of her openly and refer to her with amicability. But still, sometimes I think about how unfair it is, that my own very happy marriage is still sometimes tainted by this other circumstance I had nothing to do with, yet I pay the price.

I knew what I was getting myself into, and I wouldn't go back and change anything but still, sometimes it's just. It feels really sad in a way. And there are times where I don't mind at all about any of this, and other times where I just feel so gutted by it all. It's hard to explain. Are there any other women out there in similar situations that understand? Will this feeling ever go away?