What do you do when your heart is bursting with romantic love for someone, who you would gladly take for a romantic partner, but you and/or he or she is already taken and it is highly unlikely you can ever have him/her exclusively to yourself? What if that person was already a parent, meaning his/her children would be involved? What if that person had a very different lifestyle from yours? What if that person lived hundreds or thousands of kilometers away from you and it was unlikely you would move to live with him/her or he/she would move to live with you?
But what if that person also have many wonderful things in common with you that attracted you to him/her in the first place? What if that person made you feel better than the partner you are currently with? Would you risk committing adultery with him/her? If you KNEW that in the absence of any barriers, you WOULD marry this man/woman, would you engage in sex with him/her? Or even if marriage was not to be, what would happen?
Difficult issues, all of them. The older I get, the less judgemental I am about such things. At this stage in my life, the issue of polyamory looks better all the time.