Is this a trip for pleasure, work, or other? Sometimes that helps in identifying where the activity takes place. For me, I once worried about running into someone while out with friends who were old coworkers, in the 6th/11th house significators were the main focus.

This is a familiar question I've seen by others, and have asked myself, and the condition of the Moon and Mercury (your sig) don't promise much of a meeting here. There is an applying sextile (a weaker connection in horary) between yours and his sig and there is reception, but Mercury is in detriment and under sun's beams. Planets under the influence of the sun are in fear of what the sun represents - here the 12th house of secrets, sorrows, and self-undoing (also affairs). Moon is in the unfortunate 8th, peregrine, and opposing Saturn, the greater malefic. When significators are this weak (especially detrimented significators), you usually don't see much happen, other than needless anxiety.

The ASC so early does make the chart very iffy, and I don't put much stock in charts that have warnings like this (even late ASC is more readable, IMO). An early degree Moon isn't usually a warning against judgement, but it does show that something is in its early stages. Another warning by Lilly is when the astrologer is combust or otherwise afflicted (here you are under the sun's beams).

tribes.tribe.net/horary-as...d3c06d6c0c
I asked the question myself to see if I could get a better read, and I didn't have any warnings. The chart was a pretty clear, "no" to me. Saturn-Sun and Saturn-Moon have no future connections (only a separating square - showing a previous connections severed), and there isn't mutual reception here. Sun is surrounded by 10th, 11th and 3rd rulers (friends and maybe siblings, mother but possibly involving work - 10th ruler Venus - but seems fun in the 5th). If Saturn were a missing person, you wouldn't probably find him in a cadent house and no future aspect, and I would say the same thing here. He might actually be out of town himself, by being in his turned 9th.

Mars retro on the ASC (or in an angular house) has been much discussed in Skyscript, and it's another negative for a question. Bonnati: "The 91st Consideration is, To observe in Questions or Nativities, whether Mars be in any of the Angles of the Figure, especially in Fixed Signs; or when Scorpio Ascends, for then he destroys all the good signified by that question, or at least much impedes and diminishes it; Unless Jupiter behold him with a Trine or Sextile; for then his malice is mitigated; but yet as Jupiter is either strong or weak." Mars rules the 9th house of far away travel, and is in the sign of detriment of Saturn - so I would say this would be a pretty big no to a meeting.

Anyway, just my two cents, for what it's worth. Don't let worrying about running into an ex ruin a trip for you. Have fun!

As per astrology you both must meet. Because sextile is showing an opportunity and there's strong mutual reception between Mercury and Jupiter (Ruler Trip and Trip Trip) which makes the chances quite higher.