i'm afraid i don't know of one. i'm gonna go with though 'you've got to live life with the good and with the bad.' it sucks, and i've had many painful times i wished to forget, but i don't think there's memory loss spells. try investing yourself in something, be it study if magic, or cooking, or cleaning, or art, or whatever. i'll look around, but i think i only have spells to ease pain but not forget completely.
There are no spells that will cause you to forget a memory. However there are many other magical castings and such that can help you to deal with this memory and work through any issues that are related to the memory you wish to suppress. I suggest learning to meditate for starters. Meditation is the biggest building block or cornerstone of all magic. Through meditation you will learn to calm your mind and link your body, mind, and spirit into one. Once you can ground and center through a meditative state move on to gathering and redirecting energy. Pull positive energy into your body and push out the negative. Many do this through breathing by inhaling the good air and exhaling the bad. You can also pull positive energy into your body via your head and hands then push the negative energy out through your feet or bottom if you are sitting. After you are comfortable with these steps move on to working with your chakras. Learn to open and align them through meditation.
There are many different types of castings that can help once you have been practicing meditation and working with some basic energy manipulation. The first thing I suggest you try is shielding. Use some of the energy you have been gathering and redirect to make a wall, bubble, or whatever other object you like around you. This will help keep negative energy from effecting you from outside sources. This is useful because outside negative energy can often trigger negative emotions within us as well as negative memories we may have.
You can try casting a spell for protection specifically for protection from negative thoughts so that your mind does not dwell on this memory. A casting to help you deal with the emotions this memory causes you would be any type of "new beginnings". I don't know what the specifics of your memory is but if it involves other people and you want to be protected from them you can also cast a protection spells from people who bring negativity into your life. This negativity can be either from within or without.
I found one, I forget if I found it on this website or googling for it. But here it goes. All u need to do is chant this by heart: forgive and forget, love and let go , feelings soften feelings flow, like the river flows and flows, like the river flows and flows, like the river flows and flows, like the river finds the sea , so I flow in harmony, it's my will so make it be.
I actually changed the last part to fit my prayer,"it's God's will so make it be." but whatever floats ur boat. It works every time I use it. All u need is faith that the Universe will take care of ur needs. I hope this helps u, because sumtimes it takes magic to forget what happened to us.