Some girls and women choose oversize thick sweaters, as these boyfriend styles come usually with cable knits and fit absolutely any outfit, so you can go crazy with it, as you can try it with skirts to pants, including jeans, cropped pants, wide leg pants, pencil skirts, etc. And keep in mind, that these sweaters will work perfectly for any occasion starting from day to night, from casual to formal events (if it's too formal then it's better to pull off the sweater and stay in your formal outfit). All depends on your personal style, as an oversize sweater can look boho chic, glamor, retro or grunge inspired. Some women wear old style sweaters that look vintage and team them with posh heels and pencil skirts for an office wear.
Some women play with masculine trend, as they appear in those oversized sweaters teamed with boxy, boyfriend jeans and mix them with sleek cap and loafers. We call the oversized sweaters as menswear inspired sweaters, so if you want to style them, then get inspired by your boyfriend's images, where he's wearing those sweats.