Husband had a Provocative picture of coworker on his phone,am I being over dramatic for being angry over it?

by Jolted wife
(California)

My husband always takes great pictures on his phones,many that I do not have,every so often I like to browse and send some to myself,one morning I ask to do so, he gave every excuse not to, that he would hook his phone to my pc so I could have a larger pic to look at,I grew suspicious asked what he had to hide.After scrolling half way I stumble upon a provocative picture of a coworker of his,he claims he asked all his coworkers for a pic to place on his caller id in his phone,as they were all away in Vegas, he claimed to do this during his break@work,when he usually txts me.Later he admits he found the pic on a fellow coworkers Facebook pic kept it cause he thought she looked pretty. Their work relationship bothered me before after he spoke often of her to me, he made me think I was crazy for thinking anything! I feel betrayed by this,he claims he never looked at the pic once he had it on his phone,feel if he lied about this,why would he not lie about anything else.when you are in a committed relationship you do not take the time to get to know someone of the opposite gender and take their number down, is how affairs start.