Let me begin by saying I am sorry for this outcome after being in each other‘s lives so long. I am sure the elements of the relationship, both being together and becoming estranged, are complex, so I don’t mean in any way to reduce it to these few rudimentary observations.
The first thing that stands out to me is the prominent t-square in the composite, in the combined workings between you. And most especially the “gang up” of Sun Venus Mars all exalted by Mars in Cap and squaring, blindsiding so to speak, the inner feeling of the relationship, Moon. Sun exalts Moon, Mars receives Moon by dignity, but this is not enough for Moon; Moon has rejected this Sun Venus Mars-exalted phalanx by both reception and aspect. The Moon stands apart and alone from these other composite personal planets. The expression and nurture and support of the feeling life of this relationship is stymied.
The Moon does benefit from its reception with exalted Jup, although by blindsiding square. So this is not enough to compensate for the isolation that Moon experiences from the personal planets, which are Moon’s closer kin in the solar system.
Synastry reveals the harmonies that kept your lives weaving with one another: trining Moons, *both* of your Venuses conjunct the others’ Mars! I have to wonder if your Suns squaring might have been a contributing factor to the undoing of the relationship, perhaps some kind of battle of the wills? One Sun weakened by debility in Aq especially challenged/dominated by a conjunction of the other’s Mars? And natal Pluto hitting the Venus Mars conjunction in Scorpio hard by square and really close by degree?
Transiting Saturn (and also transiting Uranus in the lower fixed degrees) has been shaking up a number of the personal planets in both of your natal charts. So maybe it was just time for things to shift and change between you? I really don’t see these transits necessarily signaling the end. But the foundations have been shaken and I think only something new will be the result.