I've met so many people like that, they'd be one person and then the next minute it's as if they took off a mask and showed you a completely different face. This, itself, is already a red flag. This guy is not stable. This is literally proof of that. You are not selfish at all, AT ALL, for not messaging him. Honestly, the mere fact that you feel this way just - imo - speaks of how selfless you are. But as I said, some people don't see this, they just take. I think constantly thinking - hoping - that if you stay around and help him he'll show you the face he showed you before he revealed all of this will only drain you more because, honestly unfortunately, I don't think this is what it'll look like.
You are drained. This is not what a relationship should look like, any kind of relationship; whether it's friendship or more. Even if you text him, I honestly doubt it'll lead anywhere other than the same destructive cycle again.
Honestly, a couple of years ago, I felt exactly the same. I felt like no one took a particular interest in me, but this person did, and I liked that. Obviously, I saw the red flags because they were blaring right in my face, but I choose to ignore them because he liked me. Trust me, it was bad. It was really bad. I was completely walked over and used, and no matter how much I tired to help - I really wanted to help from the bottom of my heart - it was as if I was talking in a foreign language because it lead nowhere. He remained destructive - and mentally in very dark place just as AndrewSCO said - and the only thing that happened was that I was COMPLETELY drained and beyond exhausted from constantly giving. Instead of me pulling him up, he pulled me down.
Which is why I think you should move on, and pick yourself first. So what if no one has an interest in you at the moment? From what I've picked up from your post, you're absolutely wonderful and I'm very sure you'll meet someone stable and ready for a relationship. Until you do, know your worth and enjoy your life.
Obviously, this is only my opinion, you are perfectly free to do whatever you want to do!
It's just that keeping in touch with this guy, in my eyes, leads absolutely nowhere.