She hit her because of how she reacted when she caught them in bed. She also hit Howe when he was coming to her. Of course later on she realized she shouldn't be violent but let's not try to make it seem as though she's in the wrong in the situation. No matter how distant she wasn't a relationship it doesn't excuse cheating.
All of them are in the wrong in this situation. Some more so than others. But saying that doesn't mean I didn't side with Tommy. She SHOULDN'T have hit anyone, but I absolutely agree that both Tessa and Linus should have got rocked a good once for what they did.
I'm just saying that they were all young and immature, and all responded immaturely. I wouldn't want to be with anyone that hits their spouse for any reason, someone who enables and encourages cheating instead of communicating, or someone who cheats.
Let's just hope we can see growth from all of the characters.
I understand that she is your sister but that doesn't remove the fact that she knowingly became the third women. And she have to nerve to come to the girl's house and act like the girl is wrong for being mad that her boyfriend cheated on her. And her current boyfriend is acting like she's wrong for being angry that she got cheated on just because that's his :little sister". Honestly she needs to leave all of them and find happiness in herself.