Sister in law triggers me

I feel so triggered by my sister in law. I think many reasons- I make it mean that my husband and I lose our status as the cutest couple in the family. We were the only married ones for a long time, and it’s hard to get used to the new dynamic that she brings to our family. I also think its childish to feel that way, and that’s why I have so much resistance to seeing it.
It’s also like I feel threatened by their love. Because we don’t have that time anymore where it’s just us. Because I’m jealous that they have so long without kids – we had kids right away when we were married, and I think that would’ve been better because having kids was hard and changed so much in our life. It takes so much energy to be in the same room as them because I’m trying to figure out what I feel or run from how I’m feeling.