My experience is that when OW is in the picture, no information about trips and outings is usually shared. It's all very secretive.
The only thing I would caution about this is that they are secretive whether there is or isn't an OW/OM. Being a teenager means that you are secretive from your parents no matter what it is you are doing. So don't assume that just because they are secretive that something is going on that is shocking!
