should i worry when a female coworker is texting my husband more than i do in a day.....

ok first of all ive been married for 15 years this month....and yes theres been a lot of issues through out the years about trust...however i thought we were over that and moved on...well now all of a sudden i decide to look through my husband cell phone records and i see a number that not only was he texting all day and night but also calling from time to time....i only looked thru it cuz i felt something was wrong....and well i found out it was a coworker of his..when i approached him about it he simply said there just friends...however i havent met her and he never mentioned her to me at all....when i looked on his cell phone to see the name of his number on his bill there wasnt even a name it had initials on there....so im no dummy so i tell him its more than friends and i ask him to leave....he cries to me that there isnt anything there...just jokes and talking about work....wat do you think....i want to know if im the only one who thinks this s--- is wrong? o and by the way i did leave her a message and she did call me and re assured me there was nothing going on that she just got out of her marriage cuz her husband was cheating on her! lol wow are these females for real?