Hi. You said it was amicable but even so one person is usually more upset or hurt than the other. This happened to me. He provoked a fight and then broke it off. Then he would keep texting me…similar to your experience. In my case it was devastating every time he texted because I wanted to be with him. His texts were not specific about regret and getting back together. Just stuff that was confusing ,like “I saw” X” and thought of you.
I would just be starting to move on and forget about him and then he would text something and get me upset and confused again. He started to say how much ‘he cared but he could not do me justice’.
Anyway. it did nothing but cause stress to me and I still do not know what he intended, if anything. Here is what I said. ” By your choice, we are no longer in a relationship, please, do not contact me again. He sent back a one word “sad expression”. And, yay, I never heard from him again and was able to move on to better.
Stop thinking about why etc. Who knows or cares, if it is not solving anything or changing the situation. You don’t say if he has stopped messaging now, but I hope so. If not, just delete or block him and do not respond to anything else from him. I now know that for me, he was just not a great guy or match and I am glad it ended. Good luck…look forward not backward.

“It kind of hurts because it feels like the breakup didn’t mean anything to him and I don’t mean anything to him.”

This is just another version of measuring what the relationship was at its best, or whether he truly ever cared for you, and ultimately your self-worth, based upon: how much he appears to be grieving, how long it takes him to date someone else, and now — how much he pleasantly texts you as if nothing happened. You can’t tell anything about yourself or the quality of your relationship when it was good from any of these things, because we all react to loss in our own semi-unique way.

If I had to guess, he texts because he doesn’t want you to be totally gone from his life. Everyone above is correct, this continued texting isn’t helping either of you to recover from the breakup. Tell him to stop. If he doesn’t, block him. And don’t contact him. If you are truly done with him, then you really shouldn’t care what he thinks and shouldn’t be trying so hard to figure out what he is thinking.

“What the hell is wrong with guys?!” You gave permission for him to stay in contact. You never told him the contact was too frequent and bothered you. Texts are easy to ignore or block. Why haven’t you.

Now, stop girl, relax. 1. Probably he doesn’t have another thing to do, and he just walks with you because he’s very bored. 2. Probably he wants to reconquest or pass his time with you because still loves you (like you still feeling things). 3. You need to talk with him and ask for this thing, probably it’s a kind of carry-on the change and the broke up.