  In this paper we address the problem of coalition formation in hedonic
context. Our modelling tries to be as realistic as possible. In previous
models, once an agent joins a coalition it would not be able to leave the
coalition and join the new one; in this research we made it possible to leave a
coalition but put some restrictions to control the behavior of agents. Leaving
or staying of an agent in a coalition will affect on the trust of the other
agents included in this coalition. Agents will use the trust values in
computing the expected utility of coalitions. Three different risk behaviors
are introduced for agents that want to initiate a coalition. Using these risk
behaviors, some simulations are made and results are analyzed.
