regret有不及物动词形式吗？

应该是可以的，不过你说you'll regret that 是一定对的。
v.tr.（及物动词）
To feel sorry, disappointed, or distressed about.
后悔，惋惜：对…而感到惋惜、失望或苦恼
To remember with a feeling of loss or sorrow; mourn.
哀伤，悲叹：带着失落感或悲伤回忆；痛惜

v.intr.（不及物动词）
To feel regret.
后悔：感到后悔

n.（名词）
A sense of loss and longing for someone or something gone.
悲痛：失落感和思念失去的某人或某物的感觉
A feeling of disappointment or distress about something that one wishes could be different.
悔意：对希望能不同的东西的失望或苦恼的感觉
regrets A courteous expression of regret, especially at having to decline an invitation.
regrets 遗憾，惋惜：有礼貌地表达遗憾，尤其是对不得不拒绝的一个邀请而感到遗憾

及物动词 vt.

1.懊悔;因...而遗憾[+v-ing][+that]
I regret that you see it like that.
你这样看待这件事,我很遗憾。
I believe you will regret leaving Paris.
我相信你会为离开巴黎而后悔的。
I regret the loss of her friendship.
我为失去她的友谊而遗憾。
2.痛惜;哀悼;思念
I regret his death.
我对他的逝世痛惜不已。
3.为...抱歉,遗憾[+to-v][+that]