The boy her parents have found suitable for her is someone she used to date earlier. To make matters worse, I was in a relationship with his sister before I hooked up with my current girlfriend. I think he is taking revenge on me for dumping her and stealing his girlfriend.
You seem to be in one big mess with your ex and present girlfriends. The world is definitely a small place for you as you seem to be going around the same set of people. The only way out for you and your present girlfriend is to speak up. You are assuming that your ex’s brother is at work. But this may not be true as your girl’s parents have fixed the match for her. The only way to get out of the mess is to talk to your girl’s folks and settle things out. Jumping to conclusions will do you no good.