Best app to spy on someone??

Yes I know I shouldn't be spying but I have my suspicions sad to say being we just had a beautiful baby 6 months ago. He deletes his history on his phone including txts and calls..but I found open web pages 😢 I want to install something that he won't know is there..we both have androids. P.s he is home when he isn't working and he could easily be out with friends but I have found him talking to whores on POF this time I found BBWcupid...I'm soo confused and just want to know what is worth hiding or am I just paranoid..