Friendship becomes emotional sex when the feel-good brain chemicals and hormones that are released when even thinking about that person take over.
But you are having emotional sex, and that can be even more intense, sensual and all-consuming than physical sex. Emotional sex is a friendship that escalates into something that feels the same as romantic love and can manifest itself in numerous ways -- physically, romantically, emotionally, lustfully, verbally, or virtually.
Something is missing, and that missing element makes you vulnerable to temptation.
A platonic friendship doesn't have elements of sexual chemistry or attraction. In contrast, emotional sex is much more secretive and it drains energy from your primary relationship.
You may love your friend, but you don't fantasize or daydream about him or her. If you're having intimate talks and sharing things you should only be sharing with your primary partner, or you're sending late night 'just thinking of you' flirty texts, you're not having just an innocent friendship.
Pretty soon, you find yourself glowing every time you spend time with this person. This is especially true of women who produce higher levels of oxytocin -- the bonding hormone that enhances the feeling of having found your "soul mate" connection.
Any contact with the person becomes as potent as a drug addiction.