Much to my regret, I am unable to accept your kind invitation.

不能接受您的盛情邀请， 深为抱歉。

Much to my regret, I didn't have enough money with me then.

令我很遗憾的是，当时我没带够钱。

I lost touch with her, much to my regret.

【regret】很遗憾的是，我和她失去了联系。

And so my dear friends, remembering your friendly and fond good will, and your human limitations, I will close the session, much to my regret.

所以我亲爱的朋友们，记住你们的友好和善意，以及你们的人性的局限性，我将 很遗憾地结束这次课程。