casual_until_it_wasnt

Am I allowed to be angry when I agreed to casual?

Four months ago they told me they weren't looking for anything serious. I said that was fine. At the time I genuinely thought it was. I'd just come out of a long relationship and casual sounded perfect. It stopped being casual for me somewhere along the way. I didn't tell them. I just started hoping they'd noticed it changing too. Yesterday I found out they're dating someone else. Not cheating — we never agreed to exclusivity. They've actually been completely consistent about what they said they could offer. I'm still devastated. I keep flipping between being furious with them and thinking I have absolutely no right to be. They didn't trick me. But they also happily let this become sleepovers, daily messages, cooking together, holding hands in public, meeting friends... All while apparently still thinking of us as casual. Can you be hurt by someone who technically never broke an agreement? And at what point was it my responsibility to admit that the agreement didn't work for me anymore?