Trust
Gokudera trusted Juudaime with every fiber of his being. It was harsh to think that he didn't trust him back.
When Tsuna told him to trust Shouichi Irie after the whole Time Incident involving Juudaime's younger self (as well as everyone else's, including his), he had tried his best. However, no matter how hard he tried, seeing the man made him want to light a dynamite and chuck it at his head.
After all, this was the man that he believed had killed Juudaime. After Tsuna's death, day after day he had burned the image of the man in his mind, hating and wishing he could have done something. He thought that maybe if he was sent back in time, he could kill the man and Juudaime would come back, smiling gently.
Gokudera was known for his rudeness (to anyone but Juudaime), not rashness. That meant that as much as he wanted to question the Vongola Decimo, he couldn't. It could have been either out of respect of the man he looked up to for so long or just the inability to talk about his death. But, did it really matter?
When had Tsuna started weaving his web of lies? When had he first met Shouichi Irie and talked to Hibari, of all people, about his plan? Gokudera was sure that if Juudaime had asked him, he could've done anything, even if it meant being quiet.
Gokudera wondered when his boss had begun trusting someone else over his right-hand man.