why would a guy go out with someone knowing it wouldn't work out?

He is a glutten for punishment. It is the same reason women stay with guys that treat them badly. He may see it as she is playing hard to get and it makes him want her more. She made him fall in love in order to manipulate and decieve him to get what she wants. Sounds like love to him is something he gives with all of his heart and unconditionally, making him easy prey for people like her. For you the best thing is to only give advice when he asks for it and do not say anything bad about her. If you are willing to wait just be his friend and stand off to the side. She is most likely cheating on him too. If she is then you can't be the one to point it out to him. He has to figure it out on his own otherwise you will only push them together. Loyalty is a double edge sword in situations like this. Don't try and manipulate or do anything to add anything to expose her. If she is using him then she will expose herself. By saying anything negative it only makes him question your motives and places a wedge between the two of you.

The second issue I see is if the two of you are friends then are you causing some of the problems? If you want to be more than friends then consider this hard reality. He may not be interested in you like that meaning you are sticking your nose where it does not belong. Trying to get in the middle only makes you out to be the bad guy. Something I have learned recently is that just because someone tells you thier problems with anything does not mean they are looking for advice or help. In most cases they are just looking for someone to listen too, not someone to analyse it or help. Don't try and fix it if you are not specifically asked too. Unwanted help will bite you in the but every time. How can he be hurting you unless you have allowed yourself to have deeper feelings for him? Consider this, your assessment of her is wrong and your bad mouthing her is causing the problems between them because you are jealous of her. Otherwise he can't hurt you if you are just friends. She may be manipulating him but so are you,if you are causing conflict between them so they will break up. If that is the case then you are no better than she is. What are your motives? Is he cheating on her with you?

You will lose in the end because if he is cheating on her with you, he will cheat on you or you on him, or he will not be interested in you like that. STAY OUT OF IT!!

Like Ive said many times before. Treat a guy like sh*t and he will continue to come back for more. And your only hurting yourself being that you like a guy who's heart and mind are tied up with someone else.

Hey you don't know what going to happen next unless you have ESP, and who knows what is really going on behind the closed door, she has the man drooling maybe you could ask her what's her secret, do you ever remember him asking you to do something for him and you refused, she could be doing it for or to him, some guys are dumb like that, makes you wonder where their brain is really at.

some people are gluttons for punishment. others fear being alone and not being able to get someone better. others feel they don't deserve better. your friend sounds like a combination of all of the above.

Becasue guys mostly depend on looks, all they want is to go out with someone hott, you know?

Experience is a dear teacher, and only fools will learn from no other

Some people are gluttons for punishment. I'd chalk it up to that or that he is just plain ole stupid.

maybe he cant deal with the fact being lonely, give him time and when he finds the right one for him he'll come to his senses

Right now the dude your talking about is what I call S.O.S. which means Stuck on Stupid!

no i dont think all guy are like that