affor to lose him

Could you please help me understand the passage below?

Once the holidays had started, Ron and Harry were having too good a time to think much about Flamel. They had the dormitory to themselves and the common room was far emptier than usual, so they were able to get the good armchairs by the fire. They sat by the hour eating anything they could spear on a toasting fork -- bread, English muffins, marshmallows -- and plotting ways of getting Malfoy expelled, which were fun to talk about even if they wouldn't work.

Ron also started teaching Harry wizard chess. This was exactly like Muggle chess except that the figures were alive, which made it a lot like directing troops in battle. Ron's set was very old and battered. Like everything else he owned, it had once belonged to someone else in his family -- in this case, his grandfather. However, old chessmen weren't a drawback at all. Ron knew them so well he never had trouble getting them to do what he wanted.

Harry played with chessmen Seamus Finnigan had lent him, and they didn't trust him at all. He wasn't a very good player yet and they kept shouting different bits of advice at him, which was confusing. "Don't send me there, can't you see his knight? Send him, we can afford to lose him."

1. What does 'too good a time' mean?
2. What does 'had the dormitory to themselves' mean?
3. What does 'afford to lose him' mean?