You sound like you don't like to dress up, sorry for your BF. It's your choice to go looking too casual to a graduation. Leggings? Just don't go. If you want to look nice wear the dress, swap the legging for pantyhose and wear some heels. You'll look great, but it's your choice.
black leggings should be fine :) especially with the gladiators. graduation ceremonies are usually semi-formal (so you don't have to wear a dress) but it also shouldn't look like you're going out partying or going to hang out at the mall. (hope that helps :) )
The first jean is better for a fresh look. But why always pants? You can try more style, like a pretty dress with heels, updo hair. Will be cute for celebrate her or his graduation. He will be proud for your beauty!