Is your spouse cheating if they say to a coworker of the opposite sex love you too?

yes yes

It depends within the context of which he/she is using the statement. Many individuals use that phrase as a figure of speech, meaning I love you as a person, or friend, or colleague. I hear that phrase many times here at work. In fact, a colleague said that to me yesterday. That doesn't mean she loves me in a personal, sexual, or lover sense. It means she loves me as a colleague and friend. When she said this, I responded, "love you too." Now, if the individual was sincere in the fact that, "Hey! I really love you, and want a personal love relationship with you," then that would be much different. So, it just depends on the circumstances. Still, just so you know, many people just use that as a figure of speech and means nothing more.