is he cheating

okayyy so long story short i went on my bfs ig to see a nail tech since my phone was dead and i wanted to set an apt, first off he asked me why i needed it to see the phone and wat i wanted to do on it which to me was weird in general bcus he usually just opens the phone,well i go do what i gotta do and look up the nail tech in the process i see his search history he had been looking on his EX'S SISTERS page he claimed in the beginning they were friends which it thought was weird bcus when i stoppd associating wit my exs family members bcus i thought it was weird and inconsiderate to my partner this has me so upset bcus i feel like he's attracted to her or either went on the pge to try to see the sister (his ex) am i tripping or is he out of line???