How do I help my guy friend with his crush (without breaking my own heart)?

I'm sure you know there's a big difference between knowing your heart's going to get broken and it actually happening. I think all you can do is be there for him if it all goes wrong. You could talk to your female friend and explain it's ok if she does like him, she may be ignoring her true feelings if she's worried about hurting you, or maybe she doesn't like him at all. Either way you seem determined to stay close to him, which yes does mean you're a good friend, but also means you won't be getting over him anytime soon. I'd just be there as best as you can, but if you realise it's too painful don't think there's anything wrong with taking a step back. All the best :)