We all know Adrien Agreste's catchphrase throughout most of the series so far. In case you don't, here's an example:
Random person: Hey! You like Marinette, right?
Adrien: What? No! She's just a friend!
If you ship Adrienette, this might be quite annoying from time to time. But... what if there's something more going on here? What if there's a particular reason that Adrien has Marinette categorized as simply 'just a friend'? Here's my take.
It might seem a bit far-fetched but... I happen to believe that if Adrien were to like Marinette instead of Ladybug (even though they're the same person *sigh*) he'd most likely be afraid of developing feelings for someone normal, since he probably thinks that Ladybug is way stronger and has much more endurance than a Paris schoolgirl. Seeing as he lost his mom, whom he loved so much, I think that the whole 'just a friend' excuse is simply a mask over his pain of losing someone else he cares about.
All in all, when Adrien lost his mother Emilie, he also lost his father. Another addition to this theory is that he might also be afraid of losing the person he loves the most, as well as losing himself in the process. Knowing Adrien, he'd never want anyone to feel lonely or unloved. In other words, he'd never want anyone to feel like he feels and if losing someone he cares about is going to make him be that way, it probably might not seem like it's worth the risk. Those are just my two cents. Thanks for reading, folks!
-Vi