To be honest, even though he technically isn't violating any commitment agreement, your values on this are not in alignment with his. It sounds like you would definitely not go spend a couple weeks with another guy hanging out and doing stuff, covid or not.

If he feels fidelity without official commitment is unreasonable, he should just tell you that to your face and then let you decide if you want to stay with someone who doesn't share that value.

But he didn't do that. He decided it was okay to go through with his plans and make you feel bad because of a technicality.

It's not whether you're being reasonable or unreasonable. It's how he's handling it that sucks.