Oh Trent. One of the things I think Trent does is take a look at how reversing the gender roles of an ex, changes the power dynamics. Sure, you could argue that Trent and Rebecca never really dated, only fake dated to throw off Josh. But there are two things to note about that. First, one could argue that boy I kissed while we were proximal to each other tens of years ago who then broke up with me and went back to his girlfriend is just as solid as girl who found my picture, used me as a stand in and then invited me to come visit her to make it look real. Second, for every rom-com about a girl who does ridiculous things in pursuit of love, there is also one about folks who fake date and fall in love. So, really, Trent's reasoning is flawed in exactly the same ways that Rebecca's is. And quite honestly, nothing Trent has done, not researching her college experiences, not creating an intense data file, not trying to spike her wedding to Josh, and not even threatening Nathan to get her to show up somewhere, is really worse than any of the things Rebecca has done.
The blackmailing Rebecca to let him live with her and bake them appetizers is possibly the only line Rebecca hasn't crossed, and I'm not even sure that is really true. None of this is to suggest that Trent or Rebecca should engage in these behaviors. But in the framework of the pursuit of love, we have been culturally conditioned to accept that a little boundary pushing is a sign of dedication. I listened to a podcast with two screenwriters where they said rom-coms are where the hero does things that would be creepy if they weren't dating. (Yeah, I deleted the rest of that episode.) But that is a problem we are facing, there's a lot of pop culture premised on that idea. You can say it's just a movie or just TV. But it is not okay to stalk people. It is not okay to threaten their friends and family, or blackmail them, or interfere in their relationships for the sole purpose of getting that person for yourself.
Yes, the show is primarily through Rebecca's eyes, so the audience has a little bit more sympathy for her. But Trent, in addition to being a wrench in Rebecca's plans, is also a mirror.