It sounds like people have answered your question, have given you their reasoning, and have offered advice. Yet you still try and find a reason why it's okay. You're struggling with it. Well gee, get out the martyr card! You feel badly while you do something you know you shouldn't! So at least then you are already paying the price and can just keep doing it right?
In the end, no matter what anyone here says, it sounds like you've made up your mind, and are just going to keep trying to get everyone ELSE to change their mind so you instead get the validation you want.
Me: Late 30s pansexual poly. DH: My husband of 17 yrs and father of children. DC: LDR of +1 year