Is he cheating? Why would he hide it? Why doesn't he care?

My fiance and I have been together in total 6 years.. we moved to the city we in now 4 years ago. Recently he's been acting weird, very stand off-ish and when I try to communicate with him he tells me im being defensive and he's done with the conversation. I had a strange feeling recently because things he doesn't normally do.. he's doing. So.. I checked his phone and on Snapchat he's messaged a few females and has ALL females added and no males.. and a lot of them live near us... I know if I bring it up he'll get angry and tell me its none of my business.. but.. I feel sick.. mind you.. from messages I could see that the female hasn't opened he hearted her story about coming to see her at her auto dealership job. But others of course I csnt see... it goes back 4 months... my best friend accused him of cheating a while back because her coworkers claimed he kept hitting on them when he would go out drinking at their bar... he swore they were liars and we moved on.. now im not so sure.. help please.. what do you think? Also : he has 4 kids from previous I stay home and take care of every single day. while he works.

Is he cheating? Why would he hide it? Why doesn't he care?
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