Definition: to begin to reveal what you really think or feel about something or someone.
(This phrasal Verb has more than one meaning)
E.g.1: I knew she was unhappy but she wouldn’t tell me about it. However, after we had drunk a few glasses of wine she opened up and told me why she was feeling depressed
E.g.2: Don’t be so defensive – if you can’t open up to your best friend, who can you open up to?
This phrasal verb cannot be separated.