Are you knitting the left front or the back of the sweater?
The decrease should occur on the following knit row rather than as part of the bind off at the armhole. If it’s on the back, bind off 4sts, work to the end of the row, turn and bind off 4sts then complete the row. On the next row, work the decrease.
You’re correct about the yarn over adding a stitch. Because this is an eyelet stitch pattern there is a paired decrease that goes along with the yarn over. They are partners.
If you don’t have enough sts to work both the stitch pattern decrease and the yarn over as partners, then substitute the background stitch which is stockinette for both. The stitch pattern decrease (the partner of the yarn over) doesn’t count as a decrease since there is the yarn over increase.
So for your pattern, on the next knit row work the decrease then look at your sts. You won’t have enough sts to work the eyelet partners so skip the eyelet on this row and substitute stockinetter until you get to the dividing rib (maybe 4-5sts along the row). Then you can continue on with the pattern.
It looks lovely so far!