  Context. 1A 0535+262 is a high-mass X-ray binary that went into a giant X-ray
outburst in 2020. During this event, the X-ray luminosity reached the highest
value measured over the last 30 years. Aims. Our aim is to study the long-term
variability of 1A 0535+262 before and after the 2020 major X-ray outburst and
to uncover the mechanism that led to the X-ray outburst. Methods. We used the
long-term photometric light curve and the equivalent widths of the H$\alpha$
and He I $\lambda$6678 lines to monitor the state of the Be star's
circumstellar disk. The H$\alpha$ line profiles show evidence for V/R
variability, which we revealed by fitting the H$\alpha$ spectral line profiles
with two Gaussian functions. In addition, we divided our data into four periods
according to the intensity of the X-ray, optical, and infrared emission.
Results. The H$\alpha$ line profiles show single-peaked profiles in most cases.
This is consistent with the previously reported orbital inclination of ${i}$ =
$37^{\circ} \pm 2^{\circ}$. Unlike the H$\alpha$ lines, the He I $\lambda6678$
lines show a maximal intensity in October 2020, which is one month before the
giant X-ray outburst in 2020. Based on the behavior of the equivalent widths of
the H$\alpha$ and He I $\lambda6678$ lines, and the ${V}$-band magnitude, we
find two mass ejection processes from the Be star to the Be disk on MJD 55820
and MJD 56600. The V/R quasi-period is about two\, years during 2011--2015,
which is different from 1994 to 1995. Furthermore, the periods
I$\to$II$\to$III$\to$IV in the $(B-V)$ color index versus $V$-band magnitude
diagram constitute a cycle. From the behavior of the V/R ratio of H$\alpha$
lines, and the variability of the $V$ band, we believe that the precession of
the density perturbation inside the disk is retrograde.
