"Boston is going to be all love," Thomas told Sports Illustrated. "I might not ever talk to Danny again. That might not happen. I'll talk to everybody else. But what he did, knowing everything I went through, you don't do that, bro. That's not right. I'm not saying eff you. But every team in this situation comes out a year or two later and says, 'We made a mistake.' That's what they'll say, too."
"None of it made any sense. It still doesn't make any sense. I'm still asking, 'What the hell happened?' It's a trade you make in NBA2K. It's not a trade you make in real life."
Isaiah Thomas, to Sports Illustrated
Thomas' comment about what he "went through" was a reference to his efforts in helping the Celtics reach the Eastern Conference finals despite losing his sister to a car accident the day before the playoffs began, and then playing through a right hip injury that ultimately sidelined him.
Three months later, Thomas was shipped to the Cavs in the blockbuster trade that landed the Celtics Kyrie Irving.
Ainge, the Celtics' president of basketball operations, has cited the uncertainty about Thomas' injury and his impending free agency next summer as two reasons for making the deal. But Thomas says he's still puzzled over it.
"None of it made any sense," Thomas said, according to SI. "It still doesn't make any sense. I'm still asking, 'What the hell happened?' It's a trade you make in NBA2K. It's not a trade you make in real life."
Ainge was told of Thomas' comments later Wednesday.
"You know, [trades are] the hard part of the job," he told ESPN. "I know there is a lot of feelings that go on when these type of things happen. I was a player that was traded twice, so I understand his sentiments, but you guys know how much I love Isaiah. He's a great kid and I wish him the best."
Thomas helped recruit Gordon Hayward to Boston, thinking he'd be the piece the Celtics needed to get past the Cavs in the East. Now, Thomas will be standing in their way.
"Boston is going to be good," Thomas predicted. "They've got really good players and a great coach. But it takes more than talent. They lost a lot of heart and soul."
Ainge said he hasn't talked to Thomas beyond a conversation when he got traded but said he'd be open to trying to mend fences further down the road.
"I would try to [talk to Thomas], but I have no idea," Ainge said. "That takes two people and, obviously, he said some things today and has some strong feelings and strong emotions, and I understand those."
Thomas may not be able to play until the first of the year as he rehabs the torn labrum in his hip. This is just another challenge that he has faced in his career, which started with doubters wondering whether a 5-foot-9 point guard could really dominate in today's NBA.
He put that to rest with back-to-back All-Star appearances, but now he's starting over. The trade almost didn't even go through because of concerns about his injury.
"[The Cavs] hadn't even seen one of my MRIs, and they were acting like I was damaged, like this might ruin my career," Thomas told SI. "I'm not damaged, I'm just injured. But mentally it messed with me. You don't know what the Celtics are saying to save their ass or what the Cavs are saying for leverage."
Now that the deal is done, Thomas says he feels more comfortable with his new team. The Cavs aren't trying to rush him. He knows they'll be playing for June, and he just needs to be at his best then.
But he says he still can't help thinking what could have been in Boston after what he calls the "best year of my career" and the "worst year of my life."
"I felt like I was building my own thing in Boston and we were close," Thomas told SI. "We were so close! Dang! That's what hurts. We went from the lottery to the conference finals. We just got Hayward. We were right there."
Ainge praised Thomas for his efforts in his two-plus seasons with the Celtics.
"He was a great Celtic," he said. "Everybody that watched him play or has been with him in the locker room for the last few years will remember how great he was. He will be a part of Celtic history forever."
ESPN's Chris Forsberg contributed to this report.