Alpha Harlan felt the urge to wrestle with Vesper right away but he held back. If he thought thoroughly, there wasn't any basic evidence that Vesper was into Elara. It could just be his jealousness and insecurity that was tormenting him badly.
He even has Vesper grounded based on a useless reason!
"You just misused your power! And Yes! The robe belongs to me! She was here because she needed a shelter. Who is that Alpha who is comfortable with leaving his Luna to stray off in the rain?" Vesper questioned him and then answered his question with gritting teeth.
"You! Only you could do that!' He snarled and snatched the robe off his hand.
Alpha Vesper's words sunk into his head and drained him all up. His shoulders slumping with defeat as he turned to leave. "Just stay away from her," he muttered, his voice heavy with surrender.