My sister and I have an issue...?

[Michelle]

I was dating this guy named Evan for about 8 months. Then we got into this enormous fight! I may have started it and made him cry. And then the next day he called me saying “Lets not break up. Lets just forget all about it.” I agreed but didn’t respond. And I found out from my BFF Tiffany that he was cheating on me. And I was like “What?!” and she said he posted it on Facebook. (Videos, Pictures, Statuses, etc) I looked him up and couldn't find him. Then I found out he blocked me and also blocked me on Twitter, Tumblr and Instagram. I was so upset. I went with Tiffany on her account to check it out and I said “WAIT! Who is that girl??” and she responded with a snort saying “Some broad he’s hanging out with. I don’t know her name.” I replayed the video and recognized the girl. It was my sister. Evan was cheating on me with Natasha. Me and Evan are 22 and Natasha is 25. So weird! I confronted both of them about this and reminded Evan about how he wasn’t mad at me. Evan said “That was by accident! It was for Natasha!” Then guess what? About a week later, he denies that he even said "let's not break up"! This happened in February of 2013 and they’re still dating! That’s longer than me and Evan were. Evan still hasn’t unblocked me! Anywhere! I don’t know what’s going on but I do remember back in September, Evan stayed the night which was weird. I even have heard my sister say “I’m in love!”. But I don’t believe it. They never spoke or looked at each-other until after mine and evan's breakup. The worst thing is my parents never met Evan when I was dating him. But they see Evan like 3 times a week with Natasha. I even tried making Evan jealous by dating his brother, Anthony (who is 24) But he didn't care. I don’t think he’s using her. I think he actually likes her. And also, MY SISTER BLOCKED ME!! She’s my sister. I loved her and thought she was my role model growing up. Great influence my ass. I didn’t realize that a boy would come between us. She won't even talk to me anymore. TBH: them dating each-other isn't bothering me that much. That part that is bothering me is that they met each other AFTER mine and Evan's breakup. And the final part that's bothering me is how the two of them talk crap about me. I know because Tiffany has been with them a few times. And they even do it AROUND ME!! which is really dumb. But anyway. HELP! Please no mean answers. Mean answers=report. This is a serious question

[Aimee]

They're talking crap about you because they are feeling SOO guilty. Your best "pay back," I guess you could say is to act totally and completely happy when they're around. They're ok with dating each other because you're acting so miserable. And they're feeding off of that. But you know what? They will NEVER have a happy relationship/life because of what they did to you. This incident will ALWAYS be in the back of their minds and they will never be happy because they both hurt a person that they both cared about. Don't pay any more attention to them, and when your sister comes back crying to you asking for forgiveness and an apology, do it. Be the better person and accept her apology. Do not be angry. But meanwhile, you need to learn to heal yourself and forgive yourself while your sister and ex are in their relationship. Trust me, they will not last.