What are rare forms of Leukemia?

I recently made a post about a guy that I have had a thing with for a while. Out of the blue he started being distant with me and not talking to me. He also didn’t have any desire to come see me. So I thought he was seeing someone.
We started talking again but he seemed down about something. He was also talking kind of random. He started telling me he wants to have kids and asked me if I wanted to have a kid with him.
The next day(today) he asked me to Skype him. So I dolled myself up and Skyped him. The first thing he said to me was that I looked beautiful. He kept going on about it. Then we talked and laughed for about half an hr. He said he wanted to talk to me about something. I said “ok what is it?” He said “remember yesterday when we had a conversation about cancer?” I said “yes” He said “well I just wanted to let you know the reason why I have been distant and not feeling up to coming to see you is because I was diagnosed with leukemia three weeks ago.” He said “I am going for some testing by your house to decide what medications they will be putting me on, so I was thinking about coming by for a visit after”.
He said only a few people know and asked me not to tell anyone about it, as we share the same friends.
I was in shock when he told me but I believe I remember him saying it was a rare form. I don’t want to ask him because I don’t want to remind him. If anyone knows what forms are considered rare. He is 28 years old. He also said something about there being a small percentage chance of living through it. He said the percent which I believe it was 4% as his first episode of collapsing happened quite a while ago.
I know he is not lying. He isn’t that type of guy.
My hearts broken. If anyone has any miracle stories that would be nice.
Thanks