Amy are 35,my husband are 29 only,what she want?

One day,i saw my husband sms,there is a mssg received and wrote:dear,i know i am always the last one in your heart'
and i see what my husband reply,:he wrote:Not like that dear,i was busy' They call each other dear? then who am i?
Then i use his mobile to call that number,a woman pick up the call and say: hello dear' then i hang it up!
I fell so sad and cry,my body was shaking,cant control my emotion.
Later i ask him,who is the woman who call u dear,he say just a customer,call amy,nothing more? she is already 35 and have a kid,but divorce,she not beatyful one,dont think so much. I dont belive what he say,so i use my hp to sms her,i ask her,are you xxx girlfriend? i am her sister. she reply me,"i think so,if he admit. then i just tell her do you know he has married? she say she dont know,coz he never tell him. after a week,she still keep contact with my husband,i really cant stand it,i sms amy and say,you have divorce,and you know he has married,you want me to be like you?