Ok honestly can someone explain why i should ever listen to the advice of this girl?

ok so i'm 16 and a girl, my sister is 21 and her best friend is like 20. well let's call her best friend cristina. now cristina is constantly telling me to never date or have anything to do with guys because it's all way too much drama and relationships are hell. yeah i get that relationships have drama and can be stressful. but this is coming from the girl who has a boy friend who she has broken up with a million times and gotten back together with, who she cheats on all the time because she is a whore (trust me she is) and she is a freaking drama queen. she can turn a nice, calm, stress free situation into a war zone because she is such a drama queen. she adds drama to every situation. she is also very manipulative and kind of a *****. she's completely brain washed my sister, who has treated me like crap ever since she started hanging out with cristina. i have heard a million times from my sister about how cristina's boy friend did or didn't do something right or wrong and how he's always treating her like she isn't his first priority. but seriously i think cristina needs to cut this guy some slack. they've broken up a million times and she cheats on him all the time, so i don't blame him for trying to not get too serious with her and trust her too much because he shouldn't trust her at all. Cristina also flirts with everyone and anyone and once when i was with her and my sister, she flirted with a married man and gave him her number, then he called her and she just turned him down and laughed about it. i mean talk about a b*tch. And she's always talking about how she can get any guy she wants so her boyfriend should be glad she even spends time with him and it's like ok one you are definitely NOT the most attractive thing on this planet, two the only reason you can get SOME guys, but definitely not every guy, is because they know you will sleep with them and three you should be glad HE hasn't left you for good because that's coming i'm sure of it. i honestly don't like cristina. when you first meet her, she'll come off as a pretty nice person but once you get to know her you realize she is bad news. she's also pushing my sister to lose her virginity to any random guy and she is pushing her to contact her ex (which is her one boyfriend she's ever had) who totally screwed her up and was just trying to get her to sleep with him, and then eventually broke it off after a freaking month over a phone call. so yeah i get it relationships can be stressful, but when you're 16 like me you aren't looking for married, you're just looking for a cute, nice, funny guy who you can have fun with. So why the f*ck should i ever listen to this girl? And will every guy seriously make your life hell? really i want to know.