Part of it is probably keeping the love and marriage alive - it is so easy often times to fall into a rut with one another. Perhaps its then that she seeks the thrill of someone else paying attention to her? This can't be a temporary thing - this has to be an ongoing process for both of you to keep the interest alive. Have you read the book "Light Her Fire?" Small paperback book that has some great ideas for you to keep the marriage interesting. There is also one for her - Light his Fire.
Check it out.
As for the trust issue - she has to earn your trust back - if this isn't the one and only time - its going to take time for you to regain it - lots and lots of patience. Good Luck!
