venting!?!?!

This Friday while I was at work my husband took our kids to My brothers house, during that time my sister in law his wife out of the blew with my brother there they asked him that if he cheated on me while I was pregnant with my first because of how fat and ugly I got back then, my husband later told me what had occurred after I got out of work but I am shocked this is suppose to me my family and how could they say these things about me, I called them and they tried to deny it but at the end said they did say it as a joke,what kind of joke is this??!