My boyfriend David has a serious trust issue with me and my ex boyfriend Roger. There is nothing…

My boyfriend David has a serious trust issue with me and my ex boyfriend Roger. There is nothing going on with me and him and hasn't been for a while. Roger has a son named Gabriel who honestly calls me mom cause I have been there since THE DAY He came home from the hospital. We'll roger showed up here asking if I could watch gabe cause he had to go to work but he'll be off around 2-3am. I had no idea he was coming over. Honestly I thought he forgot cause he was only here one time before. How can I explain to David that Roger isn't a threat to our relationship?? Help!!