Poor Pentangeli was stuck between the proverbial rock and hard place indeed

Whilst Pentangeli should have had more faith in his Don irrespective.... Michael certainly hung Pentangeli out to dry - among others

• Pentangeli, a good old man who was loyal to Vito for years [and Michael] - who had come all the way from New York was kept waiting in the lobby to get an audience with Michael
• getting little or no help / support from Michael in his troubles with the Rosato brothers
• then Michael sends Pentangeli over to the Rosatos, to lay down to them and to settle these troubles with them
• Michael didn't bother to take care of Pentangeli's family after Pentangeli was 'killed' doing an unreasonable assignment for Michael, with Pentangeli's enemies who “spit right in his face”