How can we set boundaries about overnight guests in our small apartment?

My partner and I live in a 600 sq apartment. I have told him many times that I do not feel comfortable having his friends stay over on the couch. I work remotely and need the area for myself in the day. I told him if we had two bedrooms or a house I would be more than ok with it. I have told him many times again and again how I feel and he keeps bringing it up.

How can we set boundaries about overnight guests in our small apartment?
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