Help Mastiff biting boyfriend aggressive towards men

My 2 year old male mastiff bit my boyfriend. He’s been around him since birth but I am alpha and boyfriend isn’t. My mastiff does this everytime I am extremely upset with something boyfriend has done. I moved back home and mastiff had a fit and barked the whole time the electricians were here. I had him crated while they were here. He goes nuts barking and jumping at the door when anyone comes over. Weird thing he’s fine on walks just as long as any men do not approach us. If I stop and talk to a neighbor he’s fine as long as neighbor doesn’t approach us. Help.