Hating, or not liking someone for always winning when you are always losing; we can say is a result of jealousy, envy, and fact is, some people really don't know how to control themselves with issues like this.
Definitely if you know the level of hatred gambling comes with you'll be sure of not wanting to involve a close friend or family relatives in it and possibly on this aspects of your story that it's the friend that introduce the other to casino and from there he's been winning while the referral friend keeps loosing, like what friends allows his friend to go gambling with him and envy him at the center of his wins.
There's no big deal in that tho have seen similar issues as this and the both parties lose the friendship all because the other was doing better than the one that lured him into it. I think we should be very skeptical and careful with some friends and how we extend the friendship to done extents cause it's either remains afar than close and ruptured.
For me he did a great job but he shouldn't have nursed that jealousy habitsrather he should have asked the friend on how he went about the winnings and see how he can grab one or two tactics to generate wins and well.