technically_not_cheating

We never agreed to be exclusive, so do I even get to be hurt?

Nine months. We never actually said exclusive. I know that matters. Last night I saw a message come up on their phone from someone asking when they were seeing each other again. They turned the phone over pretty quickly. I asked about it and they said, "We never said we weren't seeing other people." And they're right. Technically. Except I have keys to their flat. I stay there three nights most weeks. I picked them up from hospital earlier this year. They call me when something goes wrong. We have sex without condoms because I thought — apparently without ever saying it — that neither of us was sleeping with anyone else. Every time I've tried to talk about us they've said they don't want to ruin what we have by putting pressure on it. I accepted that because what we had felt like a relationship in every way that mattered to me. Now I feel ridiculous. Part of me thinks they've done nothing wrong because I agreed to something undefined. Another part of me thinks they've been using the undefined bit as a loophole. Can you actually betray someone in a situationship when you never made the rules?