Where can i find a free way to track were someone is by there cell phones?

so my boyfriend keeps lying to me about where he is and i no it because people tell me they saw him were he said he wasnt...so iwant to cath him in his lie..so i wanna track his cell phone but really dont wanna pay for it...SUMMONE PLEASE HELP..cuz if he really really is doin **** he not spozed 2 do im gunnna **** his *** up :O)