Thanks for your comment.
I was taught to use the moon as the co significator for the querent and that's why I thought that I would be moon + Saturn Rx. The other person, is represented by the sun.
The question was 'Will X be back in my life within the next 3 months?' - At present, I'm not surprised that there is no aspect. As you said, it suggests no relationship in itself (this is correct), but the future aspect intrigues me and I just wondered what that would suggest.
I can see that sun is trine mars though, so perhaps this would describe the prohibition that you have explained, but then it separates and there's the trine. That's why I was wondering about the future aspects.
Date of question was 10/07/16
Time was 22:03
Place: London
There's nothing wrong with using Moon as a cosignificator in horary but it's best fully explicit about what you're doing. I always look at it after considering the two main significators when going through a reading but it's one of the first things to check on first look at the chart, as a weak Moon is itself a testimony that the thing will come to pass.
The very first thing to do is establish the two prime significators. Saturn as Lord 1 is you. But X is not necessarily Lord 7. If X were a friend, he'd be Lord 11, if he were your brother he'd be Lord 3. If he's a lover but not a 'marriage prospect', he would be Lord 5. Those are of course not the only possibilities but if you're considering him for a long term relationship, then he is indeed Lord 7. From the question X is known to you and had some form of relationship so I'll take it that he's the latter, a prospective long term partner. But, the phraseology the question would also permit you to be simply considering him as no more than a possible friend or a much less serious love interest.
Saturn is in the eleventh... a good position if you were thinking of Xc more as a future friend. Even if you were thinking long term relationship, it's a good position as it's trine the Descendant by Sign. It's also a strong house in the chart.
But if it is a long term relationship then Sun is X's significators and that's badly placed in the sixth what's more there's no aspect between Saturn in Sagittarius and the Sun in Cancer. Nor will one even begin to form till the Sun changes sign to Leo and that's 11 days off (approx). So using the main significators, the answer is 'No'.
Now for the Moon. She's in Libra,. Saturn's exaltation. I have her on the ninth, using whole sign houses and she's applying to a sextile with Saturn and will first sextile the MCand Trine the Ascendant(neither is a planet, so no prohibition) but if you use the Moon only for the current, then the sextile to Saturn shows hope but not perfection.
However there is another way the Moon can help, through translation of light. After Saturn the Moon's next aspect is a square to the Sun. The moon consecutively aspects Lord 1 and Lord 7, so now hope rises to possible perfection. Factors against perfection are that the first sextile is weak and the second square suggests obstacles and difficulties. The Moon is cadent and isn't strong in essential dignity but she is waxing. I'm not sure I'd call it for perfection but the situation isn't hopeless. He migh return but there will be difficulties in converting that into a successful relationship. If he returns then it will come down to how much you want to progress things. Do nothing and nothing will happen.