Cheating or not

So today when I got home I was watching a movie with my husband and his phone is going off he said it was his sister but the way he was taking did not sound like he was talking to his sister so when. Then about an 1 hour later he asked he to see if he’s sister has texted about a surprise party. And then I seen a message to a girl and they were flirting and sending kisses I pretended I didn’t see anything and acted normal but now I am scared and don’t know wht to do please help