Saskia
I recently did a relationship spread to clarify how a new relationship is progressing and got the Moon as how he views her. The other cards were positive so I am thinking the more "negative" meanings of the moon of illusions, delusions, lunacy may not apply. What other "positive" meanings do you think there could be? Maybe he feels she is confused about her feelings for him, blows hot and cold, is a mystery to him? Any other ideas ?
I'd suggest defining the question next time a bit differently: either
what does he see when he thinks of her? or
what are his feelings towards her?
If he "sees" the Moon, then she is the Moon - maybe hard to read, shrouded in mystery, possibly a bit scary or otherworldy, "witchy". If he feels the Moon towards her, he might be afraid of making mistakes with her (he might have self-confidence issues), there could be past relationship burns lingering that are clouding his vision and emotions in this new relationship. He might be afraid it won't work out even when there's no reason to believe that.
Typically the Moon has meant in my readings: someone's afraid without no logical reason. It's about illusions, delusions, seeing (and fearing) what is not there, due to past matters or instinctive fears. The Moon is something "not clearly seen", i.e. clouded, unclear, possibly menacing in the person's mind.