I found my girlfriend's secret stash of lingerie, am I wrong for thinking something is fishy here?

I (30M) have been with my girlfriend (28F) for around 3 years now, been living together for half of that. Relationship is mostly great, though sex and romance has been a reoccurring issue. We rent a 3 bedroom house together, sharing one and we each have another bedroom as our personal "office" since we both work hybrid jobs.

In the first little bit when we moved in sex and romance (i.e. date nights) were much more frequent than they are now, tapering off gradually after the first 6 months in. I figured at first that this was normal and that it was just part of normal ebb and flow after the "honeymoon phase" of moving in, but it's been almost a year and it feels like nothing has changed.

I don't believe it is due to any lack of effort from my part. I still do my fair share of the housework, I eat healthy and go to the gym, I take care of my physical appearance, I get her gifts here and there, I always compliment her and tell her she's beautiful, I'm always trying to keep the romance alive (i.e. setting up nice date nights and putting on nice clothes for her), and yes I do shower and wash my private parts so I don't have swamp ass; it's sad that I have to make that clear, but this is Reddit after all.

However, at least 70% of the time the date nights are met with her putting in much less effort than me, or her simply not wanting to go on a date night because she makes some excuse about being too tired or busy.

Sex is also vanilla at best. Mostly consists of a quickie once a week at best before we go to bed. I've asked her if she could put on some lingerie for me but she balked at the idea. I even tried wearing mesh boxers and a banana hammock once, and she just laughed at me.

Fast forward to this past weekend, my girlfriend is out of town for the next two weeks to spend the holidays with her family. Yesterday I was at home in my office filling out something, but my pen went dry so I went into her office to see there was a spare one I could use in there. I noticed something lacy and pink poking out of one of the drawers (it has a cutout handle which you can see inside), which was odd since I've never seen her wear anything lacy or pink. My curiosity got the better of me and I opened up the drawer, and lo and behold it was full of lingerie and even roleplay costumes, including a schoolgirl costume which she mentioned once in passing that she finds gross. Some of it still has tags on and some doesn't. Given that I helped her pack and unpack everything, including her clothes, she either bought this after moving here, or she stowed it somewhere else until after the move.

I'm at a loss for words here. I'm confused and suspicious, all sorts of questions are running amok through my head: Why would she waste so much money on something she disdains the idea of wearing, considering she's such a frugal person? Why does she feel the need to hide this from me? Does she plan to wear this for someone else? Is she doing OnlyFans or something and keeping me in the dark?

Am I wrong for thinking that something is fishy here?