Not recieving messages from only one WhatsApp contact
In order to understand if the problem is of your phone or of something else, ask your boyfriend if he sees a double-check or just one check (✓) near the messages he sent you, but you didn't receive. 


If there are two checks, the message was delivered to your phone, but for some reasons it isn't shown up. Maybe because of a malicious application?
If there is just one check, the problem is on the side of whatsapp as messages are sent to their servers but not delivered to you.