About Dumbledore 's absolute trust in Severus . And then Tonks lied . She pretended that she herself did n't know the reason why Dumbledore trusted Severus . ' But Dumbledore swore he was on our side ! ' said Tonks urgently , trying to convince herself more than anything .

Based on the preceding passage, answer the following question Why did Tonk lie to herself about Severus ?
Tonk lied to herself because she wanted to believed in Dumbledore .