Why doesn’t he change like he promised?

We broke up because my boyfriend would disappear for days without a word.
I told him I can’t deal with that and I need to be alone to think about our relationship.
He begged me to take him back. He said he would never do it again. I listened and said yes because I believed him and I care about him a lot.
It’s been a month since we got back together and he’s doing it again.
I haven’t heard from him since Thursday. I texted him and no answer. Why is he doing it again?
Why doesn’t he change like he promised?
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