Hi, I'd like to help you with your questions.
This has to be incredibly painful for you. It would be very hard to live in the same house and treat your wife the same way having this knowledge about her activities.
It does make sense that her interest in sex has increased. In any new relationship, there is an increase in desire for the other person. She is probably feeling attracted to the man she is with and bringing some of the energy home with her.
Making up lies to meet someone for an affair is very typical behavior. She has to make it sound plausible so she has the time to be away for the day. She will probably mislead you this way anytime she wants to be with him.
I am not sure why you are holding off until after Christmas to confront her about the affair- you might have children you don't want to upset or you want to try to have a decent Christmas before you tell her. That is understandable. But it does leave you to cope with the pain of what you know. That has to be difficult.
When you do choose to talk with her, the best way to approach it is to be prepared. One of the first things she might try is to deny the affair. That is when showing her the evidence you have of the relationship will be needed. That way, you can get right to dealing with why she is doing this and what the status of your marriage is instead of dealing with her denials. She may want to leave or you may want her to. Deciding how you want to react before you talk to her will help you think in the middle of all the strong emotions you both are going to feel.
You may also want to try playing out the conversation in your mind before you talk to her. Think about the things you want to get across and what action you would like to take in response to her cheating. Therapy, separation and divorce are all possibilities.
Repairing the marriage can be done if she is willing to admit to the affair, stop it immediately and attend therapy with you. She must be willing to accept the feelings you have as a result of what she has done. Anger, resentment, jealousy and sadness are all normal responses. She must not blame you or the marriage for this, but be willing to take full responsibility. Many people who have affairs try to say they were looking outside for what they were not getting in the marriage. But affairs are never the answer. The only make things worse because they undermine the trust in the marriage, which is the foundation of any relationship.
If she is willing to do the above, then your marriage has a chance if you want to stay in the relationship.
I hope this has helped you,