Dog is aggressive towards strangers

Waynesboro PA

Description

My dog is very aggressive towards my boyfriend. He’s finally started spending the night at my place but my dog goes nuts (barking, growling, lunging). She has always been protective of me but this is getting out of hand. She will take treats from him, but as soon as he is out of them she is trying to attack again. She has not been around anyone for over a year now due to covid which is why I think she’s acting like this. Are there any trainers that can help with this? And until then, what can I do to help her? She is a blue heeler, border collie, great pyrenees and keeshond mix if that helps or matters.