Please help interpret. My question was: Why have I recently began thinking of my ex (quite out of no where, probably started with a dream I had.) Drew: Knight of Cups reversed, 8 of Disks, 2 of Cups.

This is one interpretation of your three card spread.
The Suit of Cups concerns our emotional self, cups examines our relationships with others and with ourselves. Cups deal with our heart not our head. Reversed cups express our dispassion or disengaging feelings. Reversed cups also express our fantasying about what could be. It also represents a destructive love.

Eight of disks represents our earthly learning, our progress through life, in readings sometimes represents change of work, progressing through the career ladder through learning on the job or promotion through learning,
Two of cups can represent a coming together again, a reunion it tells us about bonds of love, trust. It is a card of kindness,
so if we knit the cards together in a reading I would say to my client you have been reviewing an old relationship.
At times it was not good hence it is in the past but you are mulling over the relationship and maybe thinking of it in a fond way.
As we travel through life we do review old friendships and lovers. There may be a lull in your life if you are single or a current relationship is a little flat our thoughts can turn to past lovers.
Let go and move forward, relationships are in the past for a reason, what would make it any different to what it was?
The spread tells you about the heart not the head. The eight of disks says it all, we learn, we move on taking all our experience with us on our journey.