If you're a gambler and you've been gambling for a long time, this kind of scenario is very disappointing, and that might cause you not to gamble anymore or worse, your friendship as well.
I don't have a problem with you not grabbing anymore, but the friendship or relationship at stake. I understand it's very very disappointing, even if it's your family member or your immediate brother, you'll find yourself fighting with convincing jealousy and negative feelings about the person. If you're humble and with the right attitude, you'll turn the negative to a positive.
- will you (for the sake of peace, maybe to hide your envy, jealousy) continue to go gambling with that friend? And continue to lose your money?
No.
I will stop gambling if that happens to me, but it's not because my friend is winning and I'm losing, but because I'm losing too much money that can be used in more important things than gambling itself. I'll stop giving my money to these casinos, and I will let him/her gamble at his/her own will
Well in the context, since you're always with him and he's surely securing wins, you can join him instead and do what he does, it'll relieve you of the stress of predicting your games and you'll win with him too.