It's not only an appearance. They are nice friendly people (at least the "true believers") and convinced they are doing good.
The problem is not being vegan or meditate daily. These are just personal choices, habits, belief, way of life, etc. And if you love a vegan, I bet you can happily become vegan yourself.
Your first impression reminds me my the first times with my friend
: a very open minded person, with interesting ideas on the world... during 1 month I didn't even understood she was a disciple of anything.
But don't be deluded by the tolerance they show : it's totally built up, it's fake and temporary. It's just a repliqua of the tolerance speech the cult try to spread through the websites and SupremeMasterTV ("christians, muslims, buddhist, etc... that's all same same, you are all wellcome!!!" big joke!). It's made to attract those who aren't inside yet. For those who are inside, it seems that the speech becomes much more radical, and soon or late the disciples look superior, they isolate themselves from the outsiders to avoid spiritual pollution, they are deeply convinced that their master is the best ever, their method is the fastest method in the world, their way of life is the only one which can save the planet, etc... And they will (consciously or unconsciously) serve you the same speech, because that's what they listen looping all the day on suprememastertv.
Oh yeah they are "free", that's probably what they often tell you (even before you could think they are not... just in case!) because they are told so all the days. Attack is the best defence. It is one of the most basic mind control trick : tell to someone he is free is the best way to slacken his vigilance and you'll reduce his freedom with his own approval. Anyway, considering the pressure Ching Hai put on her disciples with her incredibly ridiculous and stressful system of spiritual points, believe it, they are NOT free. They are under a constant pressure : The world is going to collapse, hurry up, meditate more give more, work more, hurry up if you want to be saved, the world need us, hurry, hurry... And also a constant guilty making process : eating meat is murder, it's bad, are you killers? you have to spread the word, the master sacrifice herself for you, you have to do your best to deserve her efforts, you don't meditate enough, you are not pure enough, purify! meditate! If not how can you pretend to save the world? Don't be selfish, find the time! You don't need to sleep, meditate instead! Etc...
For the moment your friends just avoid difficult subjects with you like meditation, en of the world, breatharianism, etc, because they know can't discuss with you. They are told that we don't have enough spiritual level to understand these reallities :) But in fact they would just fail at arguing with anyone. Actually I'm not even sure they discuss these subjects together sometimes... My friend told be that between disciples they don't need to talk, they can communicate by thought transfer (sic).
But wait until you enter deeper in thoses subjects with disciples (it can happen), and you will quicky see the limits of their reflection, their so called tolerance and open-mind.
About your girlfriend, that's your choice and we are in no position to interfere. But I guess that from her point of view, marrying with a non vegan would be a BIG issue. It's not a sustainable situation : it supposes she will lose a lot of spiritual points because of you, and will need to go meditate more and more to compensate the sin of having contact (not only sex) with a non vegan. And explicitely or not, she will continuously try to convert you, and if she can't, she may progressively get away from you.
Then, there are a few points you need to think before. Can you bear someone who watch a brainwashing TV channel for hours each days, because it gives her energy from her master? Someone who will meditate for hours in order to save the planet? Someone who argue stubbornly that it is possible to live without eating or drinking at all, and who will sometimes fast (starve herself) for a month, and become sick because she have been told that it will purify her? And maybe the worst of all : you will have to bear the pictures of Ching Hai everywhere in your house :)
Thanks no thanks.
(everything here is just my own point of view)