AIO because I found these pants in our closet

My gf and I just moved into our apartment this past August, so we’ve been here for about three months now. My lady has a foot injury from a car accident so I do most of the chores so she doesn’t have to walk.

Today I found this pair of pants that don’t belong to myself or her. She’s 4’11 so she can’t fit these. I’m skinny asf and these pants are twice as big as me. Not to mention it kind of looks like cum stains on the pants. I found them in our closet with our dirty laundry, inside out as if they were just taken off and thrown in there. There was that torch lighter and some change in the pocket.

I haven’t started a huge argument about it, I just asked the only person I know who was over, our mutual friend and it’s not his. He can’t fit them either. So I question my gf a bit and she says she doesn’t know either. Yet I can’t logically figure out where these pants and lighter came from. I don’t wanna be mad at her but it doesn’t look good.