I understand what you're going through and I sympathize. I've been there. I was anorexic in my late teens and early twenties, but I did heal -- it can be done! Keep working on your body image.
As to your question, can you be fab and fat: yes. Of course. But you have to learn to adjust your eye to see the beauty in more than one body shape.
Think of it like this. Is there any style of clothing that you hated at first but then it grew on you? An example might be skinny jeans. Lots of people hated them at first. I thought they were awful. But then my eye adjusted to them, especially after seeing them styled properly (on figures both thin and full -- thinness is not, surprisingly, a requirement for skinny jeans), and now I love them. It's a bit like that when it comes to adjusting your eye to appreciate a fuller figure. In the media, a limited range of body shapes are shown, and lean is far more predominant. Yes, we do see a few professionally beautiful "curvy" women, but even they are fat in the "right" places (think Kim Kardashian). But in real life, beauty comes in many shapes.
Also, learning how to flatter your figure, whatever shape it is, goes a long way to making you appreciate it. YLF can help you there. Baggier isn't always better.
ETA: oh, and to answer your title question -- if I'm honest, I don't like outfits that make me look way heavier than I am. It's true. But I also don't always wear outfits that make me look my thinnest. Sometimes -- often, actually -- I wear things that are, as Angie says, "just flattering enough".
If I want to look my best, though, I will wear an outfit that makes my body look as hourglassy as possible (although I'm rectangle, not an hourglass).