Sherlock(red and white) and his basenji friend Rocco (tricolor)

I've had my basenji for about a year now, he recently just turned 3 years old and ever since his "birthday" he's different.
I recently went to the vet for his health check up and he's completely healthy.

But his behavior is on a downhill spiral.

I need advice, please. This is the background story …

I moved in with my male roommate (I'm female) in December, which has been about 5 months .. Sherlock (my basenji) has only recently started growling as my roommate when he enters the living room, or kitchen .. any room the dog is in, really.
Until last night, my roommate would just carry on with his business and ignore this behavior.

But last night, my roommate came home, simply walked past my dog and Sherlock snipped at him! This has never happened before and I need to know how to fix it ...

When we aren't home, Sherlock isn't crated - he has free range of the apartment (except for my roommate's room - blocked off by baby gate)
meaning, he sleeps on the couch and hangs out there all day ...

for today i blocked him into my room and will not allow him back on my bed or couch unless invited but how can i correct this behavior properly?
My roommate never feeds or walks the dog as he is mine .. should he get more involved in the dog's life/activities or??

I know you cannot treat aggression with aggression so when Sherlock growls, we take him off the couch by looping a leash around his neck ... he doesn't like it but we have to show who's alpha ..

Any suggestions will help, please and thank you.