We develop a novel design framework for decentralized resource sharing among self-interested users, who adjust their resource usage levels to minimize the costs of resource usage (e.g. energy consumption or payment) while fulfilling minimum payoff (e.g. throughput) requirements. We model the users' interaction as a repeated resource sharing game with imperfect monitoring, which captures the following features of the considered interaction. First, the users are decentralized and self-interested, i.e. they aim to minimize their own costs based on their locally available information and will not “blindly” follow the prescribed resource sharing rules unless it is in their self-interests to do so. Second, the users coexist in the system for some time and interact with each other repeatedly. Finally, the players receive a binary feedback informing them about the imperfectly measured interference/congestion level. The key feature of our proposed policy is that it is nonstationary, namely the users choose time-varying resource usage levels. This is in contrast with all existing policies, which are stationary and dictate users to choose constant resource usage levels. The proposed nonstationary policy is also deviation-proof, in that the self-interested users find it in their self-interests to comply with the policy, and it can be constructed by a low-complexity online algorithm that is run by each user in a distributed fashion. Moreover, our proposed policy only requires the users to have imperfect binary feedback, as opposed to existing solutions based on repeated game models which require a large amount of feedback. The proposed design framework applies to many resource sharing systems, such as power control, medium access control (MAC), and flow control. As a motivating example, we investigate the performance improvement of our nonstationary policy over state-of-the-art policies in power control, and show that significant performance gain (up to 90% energy saving) can be achieved.