Bro, follow the steps below:
1) Take the dildo gently from her
2) Look at the dildo for 3 seconds, pretend to be thinking at the same time
3) Turn to look at her deep in the eyes
4) Throw that dildo into the bushes/sea or that bowl of soup if you are having dinner
5) Take her hand and head for her house/hotel
You either fuck her or you don't. If you don't intend to fuck her (maybe you don't want to betray your wife or maybe she is just not worth the effort), you would have end it there and would not have ask the question now. The fact that you are asking the question now, means that deep inside you still want to fuck her but something is holding you back (fear maybe) and you just need some re-assurance from us.