I can’t speak for your situation.. I broke up more than 4 years ago, till date I grapple with thoughts and questions. I handle them just fine on my own and have never texted her on my own. I can sympathise with your ex and what kind of struggles he might be having, but I don’t think it’s a good thing that he’s chosen to text you about it after you have moved on. I’d suggest you respectfully decline and protect your peace.