Partner says trust wasn't broken because I caught them first

My spouse (38NB) and I (36F) have been married for four years. We have been fighting over one issue and I cannot figure out how to resolve it.

They told me once, "I will never share a bed with anyone but you." This came as a result of a conversation about them traveling for work (at conferences and events). They used to have more flexible boundaries with friends (which resulted in cheating in past relationships).

They went to a work conference. When we were talking on the phone on the first night, I just had the feeling to ask "Is anyone sharing your hotel room with you?" They said "Yes, Female Friend is sharing because she had nowhere else to stay." I asked "Are there two beds?" And they said "There's only one bed so we'll share the bed." I got very upset, citing their very clear, freely-made promise: "I will never share a bed with anyone but you." They said it wasn't a big deal because Female Friend is like a sister to them. They had no intention of telling me about sharing the bed. They finally agreed not to share a bed and slept on the couch while the friend slept in the bed.

I feel like I can't trust them. Their word didn't match their actions. There have been a few other similar instances of them breaking their word. For example, this summer, they told me very clearly that they wouldn't do MDMA when they were traveling with a friend if I wasn't comfortable with it. I said "I'm not comfortable" and they did it anyway.

When I bring up how this broke trust, they just keep repeating, "Nothing happened. I didn't share a bed." When I point out that the only reason they didn't was because I got suspicious and asked the question, they said that doesn't matter because the end result was that nothing happened. When I said "I don't want to have to ask questions to make sure you're keeping your commitments" they said "Then don't ask questions." (To which I said "If I hadn't asked that question and you'd shared a bed, we'd be divorced right now"). They absolutely will not agree that breaking their word breaks trust. When I told them that I can't trust their word going forward because at this point their word means nothing, they say it's my responsibility to heal my trust issues and they have no role in fixing that for me.

I'm wondering what you think. Thank you for your perspective.

TLDR: I found out my spouse was about to sleep in a hotel bed with a friend. They say they did nothing wrong.