Homewrecker is what it is, but I look at it this way, if that person is gonna cheat with you and you say no, theyre probably just gonna do it anyways with someone else, so just do it anyways lol.
you aren't cheating because you're single so there's nobody that got cheated on. but its very tacky. would you want to be cheated on in the future if you found someone eventually? no. so just don't do it. find someone else you will feel better in the end.