I believe Dante and Trish were in it together, Trish infiltrating the Order to get information about their demon affiliation and she used the Sparda sword as a ticket inside.
I don't think so he was "Surprised" when the force-edge wasn't hanging in the usual place and in the forest he says "Things keeps getting more complicated" it means he was still unknown of trish's stupendous plan i mean without the sparda sword sanctus is nothing and thus order could've been taken down easily
she takes unfair emotional advantage from dante