Boba Fett, being educated is well aware of Jabba's abusive excess and delusion. It is only in the interest of self preservation that Fett is mercenary. He is also a man and as such, subject to humanoid desires: Oola, the slave dancer.

It is always difficult to read Fett's intent, we must look to his surroundings for insight. He is clearly attracted to Oola, this is verified by observing his interaction with the other dancers. The others are far less attractive then Oola, thus it concludes He was more attracted to her.

When Jabba feeds Oola to the Rancor it annoys Fett. Boba is cold, yet he appreciates the values of virtue and beauty. In the last year Jabba's sanity has deteriorated considerably, and his physical condition is the most obvious manifestation. The Hutt's abuses have turned him into a monster.

There is no way Lando can have worked in Jabba's palace for more then a few days without Boba recognizing him. Boba Fett is the best bounty hunter in the entire galaxy! He knows exactly what is going on, at all times. If Fett knew Callrisian was there, why didn't he warn Jabba?

When the unknown bounty hunter Boush arrives with the mighty Chewbacca, Fett's suspicions are amplified. It can not have failed to occur to Fett that the bounty hunter was quite short, nearly the same height as Liea. Lando, R2, 3PO, Chewbacca and a message from Luke, all in the last few days, the new arrival had to be Liea. With Chewie in the dungeon, Fett knew the rebel's attempt to rescue Han would end in a fight. Even though he was no longer loyal to the Hutt, it was Boba Fett who told Jabba about Liea's attempt to free Han.

When the fight at the Sarlac Pit begins Fett flies out to the skiff and aims his gun at Luke who cuts it in half. His next attack is with string, finally he shoots and misses with wrist lasers. This is the bounty Hunter who is so handy with weapons that Darth Vader made a point of telling him not to disintegrate the passengers of the Millennium Falcon. Fett was definitely pulling punches in the fight at Sarlac. He could have shot Luke with any number of lethal projectiles instead of string. When Luke jumped to the other skiff Fett misses by almost two feet, while Luke's torso does not move.

Han does not smash Fett's jetpack with the Gaffi stick, he bumps it while turning around. It is important here to recall that Luke, Liea, Han, Boba Fett- these are the most hard-core people in the entire galaxy. regardless of weather they believe in the force, they are all very much in touch with their surroundings and act instinctively most of the time. It is pointless to presume (while very possible) that Fett planed these events with Han and Chewie the night before, regardless He took advantage of the situation to fake his death. It is well known that being eaten by the Sarlac is torture because of the time one spends alive in its belly. Boba Fett's Mandalorian armor protected him not only from incidental harm in the Sarlac's jaws, but also from being digested.

Even though Fett no longer honored his relationship with Jabba, he had a reputation to uphold that would have been shattered had he actually fought alongside the rebels. Making the underworld believe him dead is clearly the best way to preserve not only his reputation, should he chose to seek another contract, also his anonymity should he chose to retire.