I don't feel like the Mary Beth/ Travis breakup was character assassination or out of the blue. For one thing, I think Mary Beth did a very nice job of articulating herself during the breakup, particularly when she expressed what he had meant to her (her first love, first sexual experience, learning a new language for him, etc) but concluded "this relationship isn't right for me anymore." There's no reason, especially when you're very young, to force yourself to try to make it work with a person who has different priorities than you do. When Mary Beth began dating Travis, he was very lonely and didn't have a lot going on in his life; he fit with her. Both of them filled a need that the other one had. His decision to join the baseball team, while understandable (especially given the already-stated loneliness and lack of anything going on), also changes his life in a very real way from his schedule to his social group.
In other words, I don't think it's JUST her insecurities that were at play here, and I think it was very mature of her to recognize that they were not only a factor in her feelings but also were likely irrational. I'm guessing that Travia WILL end up getting plotlines about new "groupie" girls and that Mary Beth just managed to save herself some time and pain by ending things now rather than waiting for the inevitable to happen. Nonetheless, as a person who is more confident and 10 years older than Mary Beth, I also would have no interest in dating someone who wanted to pursue athletics regardless. It's a perfectly fine option, but it doesn't mesh with my personality or my vision of the future. I can't fault her for having the awareness to see that early on rather than needlessly dragging the relationship out. Not everyone wants to be a baseball wife--or to see Katherine's musical on them.
Part of me feels that Travis was holding on tightly to the relationship despite also being aware that it was coming to an end. It seems similar to what Mary Beth pointed out to Bay about how she was projecting her emotions. Bay's over-concern for Travis and Mary Beth came from her concern for her own relationship; similarly, Travis' sense of desperation/ need to save his relationship seem as likely to come from a sense of anxiety that he might be growing apart from the first person who ever loved & supported him (in a romantic way). Given that he no doubt has fears of abandonment stemming from his childhood experiences with his family, it's hard to separate out how much of his last ditch effort was really about believing he still belonged with Mary Beth. He certainly offered no concrete solutions in terms of her objections to his new lifestyle (like his "groupies"). In fact, he appears to ENJOY the attention and acceptance that come from being part of an "in" group for once. He SHOULD be free to enjoy these things, but it doesn't mean that she should have to stand by him.
In terms of the Bay/Daphne plotlines, I think that Bay is actually finally catching breaks: being let off probation early, figuring out how to offer Tess support, getting her bench idea approved, and even deciding to go to L.A. Part of the reason that Bay is probably piled on is the Meredith Grey effect: people have some sort of fascination (or maybe just "show writers" have it) with watching their beloved heroine struggle against a long line of increasingly improbable obstacles. Given how superior Bay's acting skills are to Daphne's, it makes sense that she gets some of the meatier plotlines. But it looks like next week Daphne is going to fail again at her new life passion ("pre-med," everybody drink). The sorority plotline this week was pretty tame but I also enjoyed seeing Daphne get her comeuppance.