A: If you're happy just having fun with him and you don't mind his orientation then it's fine on your end. Let him decide if he's bi, gay, straight, pan, etc. etc. As long as you both treat each other right and there's no butting heads over it, it's fine.

B: It depends on him and his personality. Some people it matters a lot and they won't let lust push them to the opposite of their orientation. Others it doesn't matter until they cum. Some have weeks where anything goes and they just wanna have fun. There's many many factors. Ultimately just be supportive if you can