Why Do Guys Never Truly Love Me?

This weekend, after 18 months together, my boyfriend told me that he cared very deeply for me and that we had the best partnership he’d ever experienced, but he did not love me because there was a spark missing. So he ended things in a kind and mature way. He is not the first to do that to me, and I can’t help feeling like I am under a curse. I mean, how else do I explain why guys never truly love me?

We’re both in our 30s and the entire thing has been kind and mature and caring (and sexy and vulnerable and honest) from the beginning. I’ve dated my share of guys who were bad partners, and this guy was a good one.
And although I am hurt, I get it. I also know that he was always a little bit on the fence about letting me fully into his life. (Literally and metaphorically: Whenever I would go to his apartment there would never be a place for me to sit. He would have clothes and books and projects piled on every single one of his chairs and his sofa.)
So I kept waiting for him to start taking the actions that would let me in, and he kept waiting for the spark that would make him want to move forward. And in the meanwhile we made a fun little team.
In the end, although I am sad that he and I aren’t going to continue our team, I respect him and I get it. And, to be honest, at my core I’m feeling a bit of relief. I want someone who wants to let me in fully.
What is flooring me is the piece about how he didn’t love me. None of the guys I’ve dated long-term have ever loved me. They’ve liked me a gosh-darn awful lot, but boy-oh-boy do they not want to pull out those three little words.
And I think I’m lovable. Both in my innate humanness and in my adult life. I have my shit together. I went to a therapist as a preemptive measure because I knew this most recent boyfriend and I were about to have either the breakup conversation or the “let’s start taking steps toward building a life together” conversation, and I wanted to talk through how to approach both scenarios.
My therapist said, “There’s nothing about you that is getting in your own way. You have remarkable communication and emotional-coping skills, and you and your boyfriend have a highly evolved partnership.” She used the words “highly evolved.” She did warn me that the fact that he wasn’t physically making space for me in his apartment was a red flag, which, you know, I knew. We agreed that whatever happened between me and the boyfriend would happen in a mature and respectful way and that I would be able to handle it vis-à-vis my remarkable coping skills, and all of these things have come true and I’m still not f**king lovable? I should be cherished.
I realize this sounds like a female version of Nice Guy. I’d like to think that there’s a difference between “I’m a good person, why won’t you date me” and “I’m a good partner, why don’t you love me,” but maybe there isn’t. I also know that the big difference between me and Nice Guy is when I get broken up with, I didn’t go, “Whyyyyyyyyyy,” I went, “Okay, that’s sad, but it’s true and right and reasonable.” (Nice Guy doesn’t know what the truth of a relationship is, and I know what the truth of a relationship is. But I ache that the truth is always “I don’t love you, good-bye,” instead of “I love you, but good-bye.”)
I know I am not owed love. I also wonder sometimes if I don’t know what love actually feels like, since so many grown men have told me it’s been missing from our relationships. (One came back a year later and said, “Oh wow, I did not realize that I loved you when we dated, I am so sorry.”)
So, what is love? Why is it missing from my highly evolved partnerships? Does anyone care to answer?