Kids won't make a big deal out of something unless they see you making a big deal out of something. If they are teenagers, then all bets are off, as they live for drama of any kind
. Kids will not be scarred for life if you have a married friend, I'm assuming you won't be making out in front of them and frankly it's none of their business who you are dating/sleeping with on a romantic level. Once they get to know and like said person, they won't care. They might ask questions, which will require straight forward answers. As long as you are not giving off signals that there is something wrong and taboo, and they see he is treating you nice they likely won't have a problem with it. As parents, we tend to project our LEARNED hangups onto our kids before they even have a change to develop any hangups of their own.