is this cheating? is it worth ending a relationship over?

these are just one of the messages i found over the years we've been married. he doesnt know her personally. her daughter sung at our wedding. and she worked with him. he complimented her multiple times everytime she post a picture. and even says love u?! like wtf she is the same age as his mother. please tell me im tripping and its just my hormones. i confronted him and he laughed and said its not serious. but i said wat if i was to do the same. married men shouldnt do that. lusting after another taken women. someone save him please.