So what is this feeling that I have of sadness--like I'm trying to hold and comfort myself in the wake of this break up, even though I feel no sense of regret of my decision to not be with the person? This is not the first time this has happened to me.
It is a protective mechanism.
The thing that I have seen over and over again in my relationships is this overall performance from my lover, saying "I love you! You're my best friend! You make my heart soft!" followed by actions that go completely against that. Anytime I have been upset after a breakup, I either starve or gorge myself, stay in all day, don't want to see anyone, and overthink everything about the relationship and the breakup, trying to find some kind of peace in myself and my decisions. I'm not trying to hurt the person that I said I loved--I'm typically just trying to either take care of myself... or self-harm to make me feel in control of something in my life, while I am thinking constantly of them and upset.
But my counterparts don't do this. It appears that the minute that they break up, they move on mentally, emotionally, and physically.
I don't understand the disconnect.
I understand a disconnect if the counterpart is not actually in love--maybe I was just a way to satisfy sexual desires or was someone to hang out with when they were lonely. But in my experience, I have felt that I offer more than sex and hang outs with these people who have responded with sexual "freeness" after a breakup. In my experience, I have felt that these relationships were loving partnerships, where both partners loved and felt loved in return. So the immediate disconnect is not something that I can readily understand.
However, I do realize that people deal with grief in different ways. Maybe their version of "self-harm" or "starving themselves" is embodied by a taking control of the reigns--fucking everything in their path to prove to them that at the end of the day, they are still in control of themselves. For me, my body is my control--I can waste away and feel proud if it's my doing, even though I know it's not healthy--it makes me feel good about myself.
For them, maybe their body is their control--they can fuck beautiful, average, or even unattractive women and feel proud if it's their doing--it makes them feel good about themselves to be wanted and to be in control. It's not about knowing it's hurtful to their partner--they're most likely trying not to think of their partner in the first place. It's a state of denial of real and true, mournful feelings perhaps.
But it makes me feel as if they didn't love me at all. Ever. It makes me feel as if all of the relationship was a lie--that they just needed sex that they didn't have to actively pursue every night. Or rather that if they couldn't find anyone else to have sex with or to make them feel desired, they know you'd be waiting at home. An average Plan B.
The thing is that I could let myself feel bad about this or think of reasons I shouldn't trust or things I did to cause this. But realistically I have only ever had control of my own actions, and I'm quite pleased with how I handle myself usually.

I feel strong.
I feel like a better me for being strong.
I am free.
And I am enough.