Towards the end of season 7, Crowley enters into a contract with Dick Roman (the leviathan) to share parts of the U.S./Canada with Crowley. It seems that helping the Winchesters by giving them his blood would be breaking that contract. So, did Crowley break the contract, or did I misunderstand the terms of the contract they wrote up?
In many episodes Crowley writes his contracts with a huge range of loop-holes. In this situation it was just another Crowley-like contract where there is only one winner (Crowley himself).
It's difficult to know if it was a real contract. If it WAS, then yes, he did welch on it.
However, note the actual signing of the contract:
If you read it, you can see that if Crowley betrays Dick he forfeits all rights to Canada. That's it. It's not a blood contract, there's no threat of death or anything like that. This is why he is happy making it. Later on, with Sam and Dean, he shows he's on their side (for the time being at least):
However, ultimately this is all moot, as neither party was sincere in the contract. Shortly after, Dick Roman has the following conversation with Susan:
It's hard to know if this was even a real deal. Both parties were obviously dishonest and both parties expected the deal to be reneged. It seems more likely this was simply a fake deal designed to get everybody in the same place at the same time.
However, if it was a real deal, the consequences of reneging were such that Crowley was prepared to accept them, in the hope that the Leviathans could be destroyed.