If you'd been a better student of English, you'd know what was to come. After all, an 'equestrian' is a rider of horses, so an equestrian dildo is a dildo of a horserider.
But, in this case, the meaning is reversed. The dildo, which is the size and shape of a horse's member, is looking to DO the riding. You get home, tired, and throw the dildo on your bed, strip off your clothes, climb into bed for the night, and swiftly fall asleep.
The dildo has other ideas. It has a purpose, and that purpose is not to be alone. It doesn't WANT to be 'dismembered'; it wants to be rejoined; to be once again part of a larger being.
And there is but one being in its vicinity to reunite with...
And thus it comes to be that as you sleep, as you toss and roll in your uneasy sleep, the dildo finds itself first gently thrown free of its bag, then finds itself tangled in the bedcovers with you. And then with your rolling and tossing, it finds itself in close proximity with a neighborhood that it is very familiar with. INTIMATELY familiar with.
And thus, the dildo attaches itself once again to a living being. What once was your own phallus is now more, MUCH more, as the dildo incorporates itself into your very being. You could no more separate yourself from this augmentation than you could from your arm or your ear or your foot.
You do not awake as this takes place. You toss and turn uneasily as you become much more than you were, and your sleep is disturbed by strange and unfamiliar thoughts and images and urges.
Still, the dreams do their work. When you wake in the morning, with much more between your legs than you had gone to sleep with, the unfamiliarity is fogged by your morning sleepiness. You only really notice what is going on when you stagger to the bathroom with a much greater mass than usual pulling at your groin. As you step to the toilet to relieve yourself for the morning, you reach down to aim yourself as you always do. And reach down. And down. And down further. And as you awake, you realize that something is different. VERY different.