I think the only reason why I'm okay with Allisaac is because really, at the end the day like Melissa McCall said, you'll fall in love over and over again.
Plus, you know how many times I've seen the bro code heavily ignored? Like honestly, if people are mature enough, you can get past it.
Yes, it's fucked up for you to date your friend's ex. But you can eventually get over it, even still be best friends. Or once again, be mature enough to at least not be awkward about the subject and talk to each other in a calm manner. Without having to get so angry about it.
Scott's jealous, I get it. And hell yeah, he doesn't have to get over it. But shit, it's not like Isaac tried to sleep with her while they were still dating. So he could be just mature about it, which I guess he is now judging by the way he and Allison kind of nodded towards each other in Illuminated when they saw each other.