confused to what to do

Right so, i've posted here about my "girlfriend" before(have a read if you want of it), now we aren't official anymore, on Saturday i asked her what are we gunna do for Valentines day and she replied that she's basically busy (teaching kids dance for an hour or so, some bullshit) so i said do you actually want to be with me, and it went on and it got to taking it off facebook (shock horror) she said lets see how we are in a couple of weeks or so, SO now here is where it's gets interesting, basically i assume with good intentions that on Saturday she started talking to her ex (he appeared on her bestfriends list on snapchat) and then we argued about something (i didn't know she was talking to him until Monday) she said to me on Monday night that she was depressed and needed cheering up so, i did my best to do so, even though she mugged me off, she then told me why she was upset, talking to her ex and the good times they had, she said it's like opening old cuts, (let me say the ex is in a relationship) Now i really had no reply to this, she wants me to cheer her up because she decided to talk to her ex... mugged me off, this is only the beginning, i tried cheering up even though i really didn't want to (she has bipolar so i want to be there for her) at college today, she was sitting next to me talking to me while she was texting her ex, i tried hugging her and shit but gave up when i saw her texting him and got kinda down about it, she then turned shitty with me as i said the army are trained to kill (i want to join the armed forces just putting out there), apparently that's disrespecting her family. Now this is where it gets interesting, my friend told me that she told this guy (lets call him X) that she cheated on me, and then X went to my friend and told him this. When my friend told me this i said it was complete bullshit and it was just a rumor. Now i didn't confront her at college as i thought she was in a "bad mood" and tried cheering her up, didn't work she was pissed off with me for my comment about the army...

SO! i texted her about it, i'll keep this brief, she won't give me a straight answer and is pissed off my friends went to me first before asking her? (remember these are my friends not hers) and she's backing X (whose suppose to be her friend) and saying it isn't his fault that he can't keep stuff to him self? apparently my friends weren't showing common courtesy ? What the fuck is going on?

Now i am NOT a mean person, in no way, but today it got to me after several times saying im a mean person through out this relationship, she says i can't get on with people (haven't befriended anyone in my friends group for 6 years) and i'm a mean person and won't get into the army because of that? But that mean comment got to me, i was thinking, you're right there, talking to me while you giggle to yourself talking to your ex, the guy who ruined your life and used you (sexually)...

What is happening? am i the bad guy? or what? I know there is two sides to the story, but honestly fuck hers, i've tried sticking up for her with my friends and everyone else, and i'm just tired now, i feel like shit and it's hitting me quite hard, good guys always come last i suppose...