My Venus and Caput are on the same half of the zodiac, so Venus conjunct Cauda by secondary progression couldn't possibly happen in a human lifetime.
So, just to play along, I thought I'd check my
tertiary progressions. Perhaps this isn't a sufficiently "strong" progression system for what you want, but it's what I've got
I thought I'd found one interesting hit, but it wasn't
quite correctly timed. In late summer of 2005, I had both an important success in my life-work happen
and a (perhaps
the) critical step in one of the most important relationships of my life. Both were extremely positive and fulfilling steps, not negative. However, terts move so fast that, while Venus conjunct natal Cauda was exact when the plans for these events were coming together, it was a couple of degrees away when the events actually happened. So: Either nothing of note, or part of the larger picture of very positive events.
Back to late 1999, tertiary Venus was
stationary on natal Cauda. No relationship-related events during that time. (It was an unusually calm, stable, nothing-shifting time in the midst of surrounding years, with key changes a couple of years earlier and several years later, but not during that time.) I would expect unusually strong effects from a progressed planet stationary on a natal point, but this was... nothing.
In early 1996, tertiary Venus conjoined
tertiary (rather than natal) Cauda. There was the kind of event you are anticipating almost a year later (when P3 Venus-Node was long gone), but nothing during that time.
Now, one that is interesting - but can be taken a couple of different ways - is that tert Venus also conjoined natal Cauda oin August 1975. However, again, it just misses the mark. I had left Indiana and my wife in early June, but Venus was 3° away by then. My wife visited me in SoCal for a week in late September, and we decided to divorce, but Venus was almost 3° on the other side. My decades-long relationship with Anna-Kria began in November, with Venus long past the progression. There were a lot of points of really important relationship change over the course of six months, and they all avoided the time of the Venus-Cauda progression. (At most, there was all the reorientation and new contact stuff that comes from relocating to an entirely different place.)
Another aspect one might have expected to be of unusual importance was tert Venus on tert Cauda exactly along my natal MC / square Asc in October 1974. Nothing of note that month. (Wife and I were doing well at that point, and had relocated 50 miles, from Greencastle to Indianapolis, a couple of months earlier. No decisive events at that time, we were generally doing well. It's probably the month I started working as Marguerite Carter, so all the "new contacts" that mattered were in a work environment and were quite casual - I'd see a couple of people every couple of weeks. Oh, and we met a few people connected with the Indianapolis area astrology community, which in retrospect was surprisingly strong.)