Husband always on this app?

So theres this app called RAR. I know its an app where we can hide pics and videos. Also its like an extra storage for our phone. It showed on his phone that this app is his most use. Like hes on this app a lot. I just dont understand why hes always on this app? It does have sexy pics of me and our videos, but i dont think he would go look at it so much. Could he be saving porn to it? Or even saving other womens pics in it to masturbate? He does masturbate to porn and other womens pics. 3yrs back, he had his ex wifes sis pics in it. Im sure he uses it to masturbate to it. The pics of his ex wifes sister, arent nude. They just showed her butt, while she turned her head, looking at the camera.