It will not curdle if you cook it for an hour or longer periods of time but if you cook it for a long time, it's best to leave it on low and simmer rather than keep it boiling for that long.
I normally cook the soup, curry etc first without the coconut milk. Once the flavors all mingle the last thing to go in is coconut milk and then I turn the stove to a simmer and let it cook for an hour or so. The flavors stay a bit milder and sweeter that way.