am i trippin?

She insults him all the time in her captions. But i dont care and neither does he. When they were together my fiance was a huge help for her like he would  help her with school, bills etc. Now that they broke up, she still needs him but i told him look "if she cant at least respect you and stop insulting you in public, i dont see why you should help her or even listen to her." He said " well i dont care about her blablabla helping her doest cost me anything"

I told him no i dont want to to talk to her again, since shes acting like a b*tch. 

2Days after, i see him texting someone at 12pm, hiding his phone from me. That night i couldnt help and i went to see who he was texting, and it was her. He changed her name in his phone, replaced it by "jack" and i saw she called him that day too, they spoke for 40minutes while i was cooking. 

I confronted him about it, and now he changed his password, hiding his phone, computer, and everything from me. Im not an insecure person but i think im becoming one.. what should i do? It hurt so bad, knowing that he is lying to me, doing things i dont like in my back. I dont know anymore