You are unsure whether you are allowed to be hurt by what they did — because you never actually agreed on anything. If the uncertainty is eating at you, that uncertainty is the whole problem, and it has a fix.
Short answer: exclusivity exists once it has been said. Until then you have an assumption, and possibly two different ones. That is an uncomfortable thing to hear, and it is also the thing that explains the anxiety you have been carrying, and points to the way out.
When the relationship is undefined, your nervous system fills the gap with worst cases, and every mixed signal becomes evidence for something. That is what ambiguity does to anyone. Wanting to know where you stand is reasonable, and needing it spelled out is ordinary self-respect. Unspoken exclusivity is hope doing the work an agreement should do, and an agreement is something you can ask for.
The fact that it was never said does not settle what each of you believed; it is entirely possible you were both assuming the same thing. It is also possible you were not. The relief comes from the thing being said out loud, by one of you, rather than from decoding their behaviour more cleverly.
Ask it as a statement about you rather than a test of them: "I have been assuming we are only seeing each other. I would like to know if that is what you are assuming too." It is calm, it is clear, and it turns a guess into an answer.
Go deeper
Why You're Still in the Situationship gives you the psychology of why you are stuck, the assessments to find out where you stand, and the exact words to get clarity, commit, or walk away. Five profiles, full-page assessments and a complete script library.