I need advice

Me and my boyfriend have been together for 4 years and have a 1 year old together we’ve both done bad things together years ago.but forgave eachother.... my boyfriend is an artist he sings and makes music .. I do not like how this random girl comes out of nowhere and now they text about making music together and he’s been calling her for 20 minutes and deletes the calls so I don’t see so I ask him and he said they talked about music...this has happened 2 times already ..obviously I will get mad and try to tell him he’s wrong for it but then he gets mad which I don’t get .. anyways they have been texting sending hearts and stuff ..how am I supposed to feel because I don’t know who to talk to about this I feel mentally hurt and my head feels like exploding because I can’t talk to him about it or he gets mad and doesn’t admit he’s wrong ..if ur in a relationship u shouldn’t be sending hearts to another female or calling them for 20 minutes and deleting the calls from ur girlfriend that makes it suspicious..please give me advice idk what to do at this point ..I don’t do anything to disrespect our relationship 😕☹️