Welcome to SI. Iím sorry you have to be here but itís a great place if you need it.
At a minimum, this is an emotional affair. And make no mistake, an emotional affair is an affair. It is not "just a kiss." It is a huge betrayal of you and your marriage. Unfortunately, some wayward spouses (WSs) often lie about exactly how much physical contact occurred when confronted. You may later find out more occurred. Both of you should be tested for STDs before you have sex with her again.
You night want to consider individual counseling (IC)for her and you - her to figure out why she allowed herself to cheat, and you to deal with the betrayal. Marriage counseling (MC) is a good idea if you plan to stay in the marriage. However, you don't need to make a decision about staying or divorcing right now - even if she is remorseful, most say it's a good idea to not make an immediate decision. If she wants you, she will do the work to keep you.
She should answer all of your questions, her phone, computer and all social media need to be an open book to you. It's the only way she can rebuild the trust.
Do some reading here. Check out The Healing Library - the link is in the yellow box in the upper left corner of the screen.
Take care of yourself. This is an awful thing to go through. Remember to eat if you can, and to drink water. Exercise helps with the stress as well.
Post here as you need. We've all been in your shoes. Read some of the other's posts. Although everyone is different, it's amazing how much WSs act alike during an affair and in the aftermath.