If you felt nothing anymore, you wouldn't have tried to talk to them again. I know because that's how you know you're over an ex; you'd have no desire to return to someone you're over. But when you decide to revisit them, that's a big clue, and that you think about them more afterwards is a bigger clue. You can't hide how your heart feels.
Is it that it wasn't meant to be because of your goals, or because you're afraid of putting your heart on the line? It's rhetorical, we both know the real answer. If you can't bring yourself to be authentic, i.e. live according to your heart, you'll face that situation without the honesty that vulnerability brings, and you'll never see things work out because a cloud of dishonesty will distort everything, foster mistrust, and bring out the negatives that make things seem futile when, had you been more straightforward and vulnerable in speaking from and being of your heart, you'd see a very different outcome.
No goals that ignore the heart will satisfy you. It's why you ventured to that person in the first place; the hope of them was more satisfying. If only you decided to stop being so cautious. Without risk, there is no reward, something you'll hopefully figure out before you shut down your heart. You know, before it's too late.
That means taking that first real step, without trying to be guarded or clever. It means saying "f*ck it, what have I got to lose?" followed by telling them how you feel, as if it was the last minute on Earth. Because, in the end, you have nothing to lose by putting it all out there. At least you can then say to yourself that you said all that needed to be said. You can be at peace knowing you really tried.

You can actually choose your reality. That's up to you.

We want to be reasonable, amicable. But sometimes tighter boundaries are necessary for our own mental health and life evolution.

Impressed by your self awareness and kudos for making the choice to return to yourself.

One more spin on the dirty cycle!

What you’re saying is true. Except in this case it wouldn’t apply to me, but rather to the other person in this situation. I was always the one doing all of the things you mentioned. I just finally gave up because it was like trying to love a rock. My heart knows what it wants, but it’s not running the show anymore.

It's called the past for a reason. The future lies ahead and all you ever really have is the here and now !

I am disturbed by the advice given by You can’t let go. Please listen to your own good sense. You know what you need to be happy, and sounds like it’s not this guy.

What makes you think the advice given was by a guy? The OP doesn't sound happy at all, and if they were happy in their existing situation, they wouldn't have ventured into remingling with someone that they can't stop thinking about. In fact, the OP's lament is that thinking about them is challenging his goals. If the OP was so happy, would anything do that? No. Would they have a need or desire to reach out in the first place? No.
The only reason I can see as to why you're disturbed is because there is too much honesty in the advice you think is so disturbing. In the same boat, perhaps? Trying to run from your thoughts and don't like being told that this poor approach is going to fail? Yeah. Chew on that.

By "this guy" I was referring to the person mentioned in the original post. As I'm re-reading now, I notice OP said "them," so I stand corrected on my gender assumptions.

I commented because I get the sense OP is on the right track with their instincts and wanted to give them assurance.

OP has debunked your thoughts on the matter in their statement to you, noting that they have tried being open and vulnerable to someone who resembles a "rock."

I've been through this pattern as well—many of us have, really—and I think focusing on the self and one's own goals is one of the healthiest things we can do to recover from this lack of reciprocity.

The heart wants what it wants, but sometimes the head is needed to guide it in a better direction so that it can flourish the way it was meant to.

What you’re missing is that just because someone isn’t happy doesn’t mean they’re making the wrong choice. I agree completely with that comment as it happens, and I’m the Op. What we eventually learn in life, if we’re wise enough, is that it’s often the hardest decisions that are the right ones. For me it would be so easy to slide back into what feels comfortable. Just like putting on an old pair of boots. But that doesn’t mean that those boots fit right or were good for my feet. In fact they caused a whole lot of pain and damage that I’m only now beginning to repair. So as much as I love those old boots, I think it’s time to get some new ones.

You could have only listened to yourself.