What is my Ex thinking?

I haven't spoken to my ex in over a year. But, his new girlfriend started messaging me, which prompted him to talk to me about her messaging me. His girlfriend and I stopped talking, but my Ex and I continued to converse. After 3-4 days of texting he tells me that he still and always will care about me, that he'll be there for me anytime and that he kind of misses me...

Suddenly like 2-3 days later he just stopped replying to my messages. He saw but no reply. It's been about 3 weeks since that last text but I have no idea why he stopped talking to me...
What is my Ex thinking?
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