Why breaking up after three months hurts more than my last relationship

I broke up with my girlfriend after only three months and honestly it hurts like hell because the relationship was really good.
She was incredibly sweet. We had some differences in our beliefs she’s Christian and I’m not but we always respected each other and genuinely wanted to understand where the other person was coming from. We were patient kind and never had a single fight.
We fell in love pretty quickly which I think is part of why this hurts so much.
From the beginning I knew she wanted kids. I told her I was unsure but that I could maybe see myself having them someday with her. At three months obviously I couldn’t know for certain.
As time went on though I started noticing just how much she wanted children. She would light up whenever she talked about having kids or even when she saw them. Meanwhile I realized I was leaning more toward not wanting them and I couldn’t keep asking her to wait and hope I might change.
I sat down with her and told her that I most likely don’t want kids and that I don’t think that’s going to change.
We had a long painful conversation and eventually accepted that we’re incompatible. We both want similar things in life love each other and probably could have worked through many of our differences but having children is one thing neither of us should have to compromise on.
We’re both devastated.
She was the first person I dated in three years. Before her I was in a seven-year relationship and I spent the last three years focusing on myself and trying to become a better person and partner.
Then these three months happened and we shared so many good memories. We had so many plans and genuinely thought this could become something long-term.
I want her to be happy even if that means she has to find someone else. She deserves someone who is completely sure they want children and I know I can’t promise her that.
The strange thing is that this somehow feels harder than getting over my seven-year relationship. My previous relationship ended because I was hurt. This time nobody did anything wrong.
It’s just two people who genuinely love each other had something really good and still had to walk away because they want different futures.
I know this is probably going to take me a long time to get over. I just hate that sometimes love and compatibility aren't enough.