Just my two cents again, but I feel like Ally and Teddy’s affair was incredibly unnecessary - to the plot or otherwise.
I get that Wallace was supposed to realise what he’d lost, especially if someone else had what (or rather, whom) he once did. I also get that Teddy was intended to be the more sympathetic of the duo.
However, did she really need to run into another greasy nerd’s arms to seek comfort? And whatever tf happened to the option of just leaving Wallace? Might just be me as cheating is one thing I’d never tolerate in a relationship due to deeply personal reasons.
With Wallace, it seemed as though she were putting up with him as she’d known him for a while and living in hope of him going back to the man he once was. :( But cheating on him as well with Teddy was just redundant and even stupid.
Even if she stayed with Wallace as in the movie’s original events, there really wasn’t any need for her to get with Teddy. They could’ve just been good friends, which explains them searching for Wallace together.