Hi LiJ, This is an interesting question. My dictionary doesn't offer a separate
adjective listing.
You can use it as a stand-alone.
Are you with us on this? (reply)
Yes, I'm committed.I think your web examples are incorrect. When it has an object, I believe "to" is required.
He's committed to affirmative action. "To" is a preposition, right?
So if you wish to use the infinitive as an object, it seems to me you'd need a second "to."
He's committed to to leave by four o'clock. Perhaps that's why we choose the present participle (gerund):
He's committed to leaving by four o'clock. I have no idea what the official word is on this.
Best wishes, - A.