The John Legend you-can't-top-this-date-my-future-baby-mama was a swing and a miss. I enjoyed it, sitting at home, liking John Legend, but dudes, just no. Oh. Unless Kevin's alcoholism is manifesting itself in "drunken" escape-from-reality dating methods. Then, I stand corrected.
I don't mind Jack flashbacks. I know where they started and where they ended, this is all filling in the blanks and I kind of like that. Otoh, Rebecca's (uh-oh, I couldn't remember her name) mother's little speech was all kind of bullshit from that character. And as much as I enjoy Jack and Rebecca's story (thanks, Milo and Mandy), they can jettison the "love for the ages" trope right now. Stop it. Seriously.
The characters' flaws make relating to them deeper, you're doing a good job, writers, you don't need to create a Camelot here. Or a bad soap opera.