Is it okay to say goodnight sweet dreams to a coworker?

I went through my husbands phone today not really expecting to find anything . He's been hiding his phone lately if hes texting someone and.im near he does that when he's texting his best friend ,which isn't super unusual.He's been texting someone new I guess. Anyway I got his phone to turn on roku ,but had the urge to look and well hes been texting a female coworker and it seems platonic at times, while others it seems he's interested in her and her him.He's been to her house apparently .She forgot her name tag in his car. She texted him " I'll put you in 7 different positions in 70 minutes " but then said it was lyrics from a song after he responded with "???"idk what to think .Hes been to her house apparently. She left her name tag in his car. Then he caught me with his phone and I tried to pretend I didnt look through it cuz idk what to think amd was trying to process what I just read.which he tried to be sweet and affectionate. Which for some reason got me mad and he kept clinging on to me . Telling me he loved me and part of me thinks there was more that I didn't see .am I being paranoid ? He actions were suspicious or am I wrong?Is it wrong for my husband to tell his femal coworker "goodnight sweet dream"?