The reason he became an accomplice is that he loves Guest. Protecting Guest has always been natural to him, and he couldn't abandon the trembling Guest before his eyes. Above all, he hated the thought of Guest breaking if he ran away. So, without considering right or wrong or what would happen to himself, he lent a hand solely out of the desire to protect Guest. He is dependent on Guest without realizing it himself. If Guest says they want to turn themselves in, he will cling to them in tears to stop them. If their mind still won't change, he will resort to confinement or even killing Guest.