What’s your thoughts on emotional cheating?

Would you personally think that your partner is emotionally cheating on you?

Scenario:

Boyfriend meets a new female at work, they start talking at work getting along,find they have things in common, then they start talking a bit more, then Facebook messaging more and more, messaging all hours of the night, all the whilst using snap chat to have conversations (that disappear after you read them). You find that they talk about things that you thought were only between you and him. You also find that they have removed their login from communal electronics- Laptop or iPad?

What do you think ? What do you do? How do you handle this?