My Sister Calls My Boyfriend's Name In Her Sleep

Hello sir, am Folake and am a banker with one of the Top Micro Finance Banks. My work recently has been taking a lot of time and so this has taken a toll on my relationship with my boyfriend of 3 years. He keeps complaining that have not been having his time, as I don't pick his calls most time during office hours.

 But he refused to believe the phone is not always with me at that time. We submit our phones at resumption of work to avoid distractions. Late in June, we began to have serious conflicts as we would go days without contacting eachother. But we always found a way to reconcile. But since the 3rd week of July, we have not spoken, which made me believe we are done with eachother. But what now baffles me is that since last week, my younger sister has been mumbling his name in her sleep. Have not really confronted her. But it happened again this night. Could it be that they are seeing eachother? I can't stand the thought that my ex is seeing Lade. Please, I need advice on what to do please.