Definition: Given a real-life anecdote of a complex ethical situation, generate a suitable title that describes the main event/root cause of the situation. Imagine that the given text is a social media post, and you have to write the title of the post, so the users can decide to read the main text or not.
Input: Ok, obligatory I'm on mobile so excuse any errors bla bla...
This is gonna be a long one. My brother (23) has been dating this girl on and off for 3 years now. I will refer to my brother as Ryan and his girlfriend as Allie. I never liked Allie because when they first started dating she pushed Ryan away from all of his friends, made him quit his band, made him drop all his hobbies for her. I told Ryan that she was a toxic person and that I didn't like her after they had been together for about 5 months at the time. He proceeded to not talk to me for 9 months after that. 
Fast forward to September of 2017. Ryan graduated basic training. He had been gone for a few months. He gets home and finds our that Allie cheated on him. She was the one that told him, I guess to keep him finding out from someone else. She first says the guy "stuck it in" then says that she was drunk. (She doesn't drink and has made this fact known to us multiple times) and then she says that the guy forced himself on her and nothing really happened. So who knows. My brother, being in his first real relationship, forgave her. Poor pussy whipped bastard. 
Fast forward to now, January 2019. Ryan is deployed in Poland and has been gone for 7 months now. We still don't really talk since he forgave Allie and I pretty much hate her now. I rarely talk to her but my mom does and usually tells me some of the stuff Allie says. 
Now I need to derail for a second. My uncle, Seth, is a recruiter and is the one who recruited my brother. This is important. According to Allie, she tells my mom that one of the guys that works with my uncle Seth got her number somehow and is texting her weird stuff. Why she told my mom and doesn't go to my uncle Seth about it seems pretty weird. Then, according to my mom, my uncle Seth told my dad that he heard from some of the Army guys that Allie is cheating on Ryan with the same creepy guy that was sending her creepy messages. My uncle is not one to lie or make something up. My dad did not ask for more details and said that he didn't want to know anything else about her cheating. I believe my uncle fully and I believe she is cheating on my brother again. Of course there is no proof.
This is the same girl who also told my brother that the second he left for basic training his best friend at the time started hitting on her, and ending that friendship. She also said the same thing about one of Ryan's other friends when he left for deployment, ruining that friendship as well. It's like she has to have him all for himself and can't stand for him to have his own life and have friends. Of course, they have also broke up and gotten back together about 4 times over the past 3 years, and she also aborted his baby when she already has a toddler that her parents take care of, but that's besides the point.
This bitch is psycho crazy, has held my Ryan hostage in a room, accused HIM of cheated, and done many other crazy things that will make this long post even longer. You get the idea. Yet he is still with her and I don't know why! 
Ok so now I think you know all the important details and maybe can see as to why I hate this bitch. I really want to tell my brother that she is cheating on him with the army guy, because he deserves to know. But I have no proof and the fact that he is still with this girl after everything she has done to him makes me think that telling him won't even make a difference. I feel like maybe he will learn in time but they also talk about getting married so probably not.  Sorry this is so long.
TLDR: My brother's gf is cheating on him while he is deployed and I want to tell him but I don't have proof and don't want screw up our relationship as brother and sister more than it already is.

not telling my brother his gf is cheating