I think in this situation, it is always easy to lay blame at one person's door - as most people on here have already done.
As someone stated, it is impossible to live one's entire life morally, so "bad" things are done by us all.
Who makes the rules that we can only "love" or "be in love" with one person?
Society has generally told us that that is the norm, that we fall in love and marry one person.....but what happens when one falls in love with two people?
It may not be the "correct" thing to do, but there are times in our lives that things happen that we cannot control.
We cannot control our feelings - be they feelings for an item, a pet or even a person - therefore, we cannot control who we fall for.
This guy has, from what you say, Dakota, fallen for your friend, as well as still loving his girlfriend (i would assume). The two women in his life are probably very different in most ways - hence the reason for him falling for both.
They offer different qualities as people and this is what may attract him - in general culture, this is regarded as wrong, but why?
I dont want to open up a new kettle of fish about bigamy or monogamy, but, like i said, you can't help who you fall for.
I dont come on here too often, but when i do, i see so many self-rightious people, preaching that they know best and making out that the subject of a question (like the guy in this one) is heinously out of order.
No one is perfect and no one person has the right to preach to others when they, themself, have done bad in their life!