Do you thing a kiss is cheating? Story below

So, my husband told me the other day that he kissed another women. 
The story: my husband and I work together, and we have a friend/coworker having a really hard time in her marriage. We invited her over to help her out. We were sitting around drinking. Later in the evening, I went to bed leaving my husband (whom I trusted completely) down stairs. The coworker was getting all sad and saying how lonely she was. So my husband put his arm around to comfort her. And it happened, they kissed. He cannot tell me who kissed who. It just happened. 
Now, the reason he told me... We are ttc and Could be pregnant. 
So please... Any advise is welcome!!!!

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