Yes I think so even though usually I think the idealization and especially the devaluing phase are really long in this case, maybe a little too long for this.
So I would say other factors might be involved too...
If we would change years to months then it would be more likely.
Also a lot of things must have happened after that mistake...
What kind of mistake was that?
I don't think no phase is that long...
This is a slow process, that takes place over the years, not an abrupt ending which would be more likely...
Also if someone with BPD fears abandonment usually all efforts are taken to prevent a termination of a relationship - even if it is not functional, damaging or just not all roses and butterflies anymore...
Communication is better than assuming or looking back on things and dreading the outcome.
Since you already use these terms you seem to be informed and the partner is officially diagnosed.
Especially frequent, intense fluctuations would indicate the typical idealization-devaluation pattern which I think cycles more frequently, the more unstable the individual is.
Again, I think BPD is not the only factor to blame here if at all.

I hope you are dealing okay... This must be hard to deal with.