as how to read this - the line at 2 degree is when the aspects "come in", they then get more momentum until they reach the peak, and then fading out. Westran uses a 2 degree orb for his study, but sometimes the orb is smaller than that, but 2 degree seems to work as a general figure.
Also the degree before the peak (which I guess often relates to the year before the peak, but it depends on the duration of the aspect) is when the aspect is the strongest/ most intense, and sometimes you can feel it fade away sooner than at the 2 degree orb, at least yuo might experience a decrease in intensity, not sure when this sets in, I guess there will be a bit of an aftermath, but the separative phase is usually weaker or not as intensely felt, but again, it depends on the overall picture.
As for the aspects, at the onset of relationships the trine (in particular), conjunction and opposition between Sun-Venus, Venus-Venus and Venus-Mars were observed to a very high level, statistically dominant. There seems to be a difference between pr - pr aspects, and pr- natal ones. Also it seems that the pr-n Sun-Venus trine as well as Venus-Mars-trines of any kind were the surest indicator of affairs that probably did not lead to marriage. However that is not necessarily true (my parents started with a double Venus-Mars conjunction, pr-pr and n-pr and they got married, didn`t they? I do think however in their case it might have played a role that this Venus-Mars-conjunction fell exactly onto my Mom`s SAturn, which rules her DESC, and maybe it also meant something that it fell on my Dad`s SN, so by means of that attraction scenario their Saturn-SN-connection was activated. Yeah there you meet someone and think this could be a nice affair and then you are hooked for life. LOL)
Anyway without making a difference between natal and progressed and progressed and progressed
Sun-Venus is the singlemost frequent occurrence at the onset of relationships, it brings attraction, harmony, agreement (in the trine at least), cooperation etc.
Venus-Venus is very sweet, gentle, kind, loving, adoring even, but the setback is that you need something stronger to activate this, some Sun or Mars. Venus-Venus could go on loving each other forever without even verbalize it to the other person.
Venus-Mars is well, you know, passionate and sexy.
it turned out that the sextile and quintile (at least between Sun-Venus) were quite relevant, too, not as often happening than the louder aspects (trine, opposition and conjuncton), but significantly more often than expected.
The sextile has a friendly vibe, and often indicates people getting into a relationship after being friends.
The quintile is a little more playful, quirky and creative, a little spark of magic is added.
While he did not mention it, and I guess it did not come up too often in the study, but I`ve come across quintiles between Venus and Mars and also Venus and Venus so often in those synastries I have been looking up. It is odd, considering that it still is considered a minor aspect. I will keep on observing this little maverick-aspect for sure.
There are two squares that most often happen at very difficult times in relationships.
Sun-Venus, which is dubbed the "Romeo and Juliet" aspect; it is separative, not because of a lack of attraction, but usually because of external reasons. People being kept from each other for other reasons than a lack of attraction between them. Sometimes society stuff. Parents. Long distance. Whatever one could think of. This one sucks so much, cause while being kept apart (esp. if there had been a better period before), the people might still feel very strongly about each other, so this one really hurts. Apparently it is mostly the Sun-person who is hurting the most (but I would treat that sentence with caution, just putting it out there, cause I read it and I am not totally convinced, that this might not be due to other aspects happening simultaneously).
Within relationships, this can either lead into a separation, being kept apart, or it just signals difficult times. For example my parents had this one in a very difficult period in their marriage, when my father was working very hard, and my grandfather had a stroke and my mom was basically becoming his nurse 24 hours a day (and also looking after her mother in law and us children, of course my Dad helped as much as he could, but he had to bring home money, too). So in a way they were literally being kept apart from eacch other (to a degree), while still being together, if that makes sense. Ironically (and cruel irony at that), their Sun-Venus-square went out of orb or was at least a while after the peak, when my grandfather died, and they were after a few months taking a second honeymoon trip (it was their 25th anniversary) to Norway, which was obviously a very happy trip.
That is the other side of Sun-Venus-squares in progressions, obviously once it has gotten past the peak clearly and gets out of orb, there can be a release of tension felt, and that might actually feel just as positive as a positive Sun-Venus-aspect, at least for a time after.
then there is Venus-Mars, which Westran calls "the killer aspect", of course it does not kill the relationship every single time it happens, but apparently this one was almost as reliable for indicating the relationships end, as the Sun-Venus trine was indicating of some relationship forming.
The problem with that aspect is that it indicates a dysfunctionality inherent in the people themselves, and often at least temporary incompatibility, and one or both people making choices that will jeopardize the relationship, or as Westran stated: "often the choice is in betraying the partner". So third party situations, probably not only the lover/ mistress-scenario, but this one definitely, too, and other stuff that just blows the relationship apart from inside.
Now personally I believe, that yes, of course relationships can weather this aspect, as well. It depends on the people of course, their ethics etc. For examply my best friend and her husband had that, and she did report a difficult time afterwards, with eeach of them flirting with the possibility, if oyu know what I mean. It never really went that far, but they were growing apart for a time, for some reasons. However, they eventually were facing that, sat together and talked it through, and then worked it through. Divorce would not have been an option for my friend, not only because they have 5 kids, but also because of her mindset. Well of course they still cared about each other, so that was helpful too. But it was difficult to navigate this.
However they also had simultaneously a nice Venus-mars-trine and either a Venus-Venus or Sun-Venus-aspect, a harmonious one. so I think this aspect probably mostly "kills" a relationship if ther eis nothing else or nothing strong enough to counteract it.
In P`s and his old gf case there were a Sun-Venus-square and Venus-Mars-square happening in the same year, well Venus-mars-happened before, but they had almost made it through, even with Sun-Venus-starting, but then a Venus-Venus-sextile went out of orb (doubt a sextile would have been strong enough anyway) and that was exactly the time they split. The exactness of the timing was actually downright creepy.
well that is how I understand it all. I might be wrong of course.