My ex boyfriend always tells me he's sad and unstable?

My ex and I have been on and off for about 2.5 years now. I went on vacation last week and he randomly texted me that we should stop talking. I said okay and didn't contact him. Whenever he contacted me, I ignored it or replied with a simple answer. He constantly texts me saying he misses me and he's emotionally unstable. I don't know what to reply to him because I asked him if he wanted to be with me but he said "not now." I don't understand him. Please give me some insight