Personally I prefer if he reveals right away and explains he just wants to live peacefully, Twilight considers that he just took care of her when she was vulnerable and gives him a chance while strictly keeping an eye on him. And then because she knows he needs love but doesn't want to leave him randomly hunting and also she is a young mare with needs and as different species he can't impregnate her, she decides to make some love. ;) Though I expect that bit will be much longer in lead up.
Personally I prefer if he reveals right away and explains he just wants to live peacefully, Twilight