The fact that B will even be in a toxic relationship with a person like T is something to take seriously. It's a big red flag. I have been exposed to similar drama and it was enough to make me walk away- even though I was madly in love. I am probably a good bit older than you and I have learned that it's best to walk away as soon as I see signs of that level of drama.
The key to life is in being fully engaged and peacefully detached simultaneously and authentically in each moment.