He deeply regretted this loss.

I regretted doing that as soon as I did it.

I very much regretted having lost so much time.

She bitterly regretted having said something that displeased her mother-in-law.

He said he regretted the decision.

I regretted the decision.

They regretted lying.

Tom said that he regretted that he couldn't help Mary do that.

Mary bluntly refused the gift that Tom, her mother's new boyfriend, wanted to make her. Later, she regretted it.

Tom instantly regretted what he said.