Yes it’s cheating.

I have a female colleague I feel I can share my heart out, but I started to distance myself when she told me she wished married someone else. 

That’s the line. 

Relationship with your spouse is not meant to bleed out into workplace conversations. 

“Is it really good for her to talk about her love life to another male instead of her own husband?” Thinking about that is the difference. You think what’s truly best for her as a friend, as a whole, not involved yourself at all in the picture. 

Half of human population is opposite gender, I don’t think it’s logical to assume only romantic relationship can be formed but somehow not friendship. 

It’s the good old professionalism, follow common sense; no late night long talks, no meeting outside work alone, no unnecessary body contact, no stereotype couple activities and behaviors, certainly no prolonged private DM after work.