I need your help! My brother is boning a landwhale and I don't know how to deal with that. My brother has recently brought home his new "girl"friend, who he has been dating for about 2 months now and who is definitely in the top 10 (if not top 5) fattest people I've ever talked to in my life. Ever since he brought her home, I've been thinking about how to tell him that he is literally making the biggest mistake in his whole life. But I don't know how. I've been living in a flat with him for several years now. We play together in 2 bands, have been playing in bands together since we were teenagers. We're both in our mid-thirties, 2 years apart, both about 6 foot tall, I'm at a BMI at about 20 (trying to slowly get it higher without adding fat), he has always been the "stronger" one of us both (the heavier one) and I guess he is starting to get into overweight territory and if he continues to date his new girlbehemoth, he will definitely continue to gain and become obese one day. He's a guy who has always loved big tits, so his past girlfriends have all been at least a little fat, some more some less, but all definitely way too fat for me. I never really did mind because, hey, I'm not the one who has to see them naked or get a boner, and I think it's none of my business what turns another person on or who they spend their time with. And they all had at least a nice face and personality and I got along with them. So I tolerated their fatness. But this new one... I can't even look in its general direction because of how grossed out I am about how fat it is. Its fucking gut pertrudes further than the sacks of mayo one might call her "tits", and her face is everything but pretty. It's fatness has made me lose appetite and made me work out more, because I don't wanna end up like it - my fatphobia has been fully triggered. I just can not comprehend how anyone would voluntarily look at it naked, how any man could get anything close to an erection within viewing distance of this bag of lard. I can't even overcome my repulsion to even try to get to know it better. Hell, it's my brother's girlfriend, I feel like I should give it a chance to prove that it might be a human – but I can't even look in its general direction without being disgusted. The most facepalm-y thing about it is that he met it on a dating site... that he is paying for. Who gets fatfished on a paid membership site and still goes through with it? The most enraging thing about it is that a few years ago, my brother discovered climbing and started to eat healthier and got ripped. So much so that he was one of the reasons why I went from skinny-twig-arms-with-a-little-belly-and-a-coke/icetea/potatochips-addiction to skinny-with-defined-muscles-and-decent-eating-habits. He kept eating healthy but stopped climbing regularly. He's not fat yet, but will be soon. I've never talked about FPH with him, but he has an idea about my opinions and feelings towards fatness, fatlogic and fat people. I believe this is why he never showed me pictures of his lardfriend and kept sleeping at its place for a month before daring to bring it home to us. Or maybe it has to do with the fact that we live on the 5th floor without elevator. I somehow have this weird hope that they might be trying to lose weight together. He has asked me if it is normal to gain more than 1 kg in a day and thought that our bathroom scale might be broken, he has started eating salads and cooking more vegetable-y stuff instead of eating bread with cheese or hummus at home. The problem there is that he uses sooo much oil and butter and cream and cheese and needs a lot of bread along with the salad, that I am starting to think that even if they both are dieting buddies, they will both fail because of how much fat they add and because of the sheer amount they both need to feel full.  Oh, and they drink a bottle of wine every single evening. It's like their thing, even when they're just skyping. I have the feeling that she will drag him down and implant first fatlogic, then fat acceptance into his mind. I think I need to intervene before it's too late and I am the bad guy hating on his fat girlfriend in this story. How can I open his eyes to what he is doing, how unacceptable it is to romantically associate with somebody who clearly either doesn't take care of herself or is too stupid to see what she is doing wrong in her life? I can't just disapprove of who he is having sex with, it's none of my business, but this needs to stop. I am starting to question my brother's sanity. tl;dr: brother who i live with is dating an unacceptably fat landwhale, how do i tell him without being an asshole that this is a mistake he should not make? [EDIT] 6foot tall instead of 2