Trusting someone is different from being cautious. For example, you may trust your best pal but you're definitely going to be on your guard if you're in a dark alleyway at night to meet your friends' friends.
Additionally, he has that hero complex of his and by the time Liz dropped the invite they were already pretty far out. No way he's just gonna let a noob go back alone when death means that people die when they are killed. Besides, IIRC party members can't attack each other so getting stabbed in the ass is no worry.
Even more so, back then he was only accounting for himself. Now he's accounting for another and his hero complex.
That about cover everything for you?
EDIT: If not, I'll get back to you after dinners.