Unless you had some bizarre case, or an awful doctor, you would know if you had a torn bicep. You'd be in surgery a week ago.
You may need to go very light on the bicep curls. If it the left bicep is smaller that's a sign your bicep could use some work. However, you'll need to loosen up the posterior capsule first. If the posterior cuff is really stiff the shoulder can't glide backwards well, so it glides forward which puts pressure on the bicep = pain.
What are you doing in PT?
I wouldn't be overly concerned with an MRI. If you've been an active person for a while chances are a shoulder MRI isn't going to look good no matter what. That doesn't mean you need surgery though. Nobody really has an idea what "normal" should look like on an MRI for shoulders. Something like 80% of baseball pitchers have tears in their shoulder on an MRI but only 14% are in pain. It's a horrible indicator for whether or not something is really wrong.
Quoting James Andrews (world renowned surgeon) "If you want an excuse to do shoulder surgery on a baseball player just take an MRI of his shoulder."