Yes, it most assuredly is a question that needs answering and your marriage doesn't stand a chance if she's still in contact with OM.
And, if you don't know that she isn't in contact then she probably is.
Hope4us is absolutely correct. Complete and total no contact is the very first requirement for recovering your marriage.
Don't let her back into your home until this has been dealt with. Other posters and bitter experience has taught me that it's a very, very bad idea. My W came back to live with me and stayed in touch with OM, even visiting him a few times. I am dirt ashamed of myself for this - I basically offered myself as a host that she could parasite off of. Don't do this my friend.
No worries GH31, I will not put myself back out there unless I am given complete assurance OM is gone for good. Given that we are separated, it may be difficult for me to completely verify it, so at some point, I'll have to trust her. I don't want her moving back for a long time, not until we are very very solid with each other. I will not put my kids through a failed reconciliation, so I will be very careful about this. I do have the advantage that OM is thousands of miles away, which helps somewhat.