Hello! This is my first orchid and I'm really trying to keep it alive. It was delivered to me as a gift back in March and it is now end of May. The flowers have been in bloom since it arrived. This month they have started to fall one by one.. it almost looks like the flower is closing before it falls completely off. They have developed these dark spots on the back of the blooms, and the leaves have also taken on this darker color. After watering, the leaves perk right up but they still remain darker. There has even been a new leaf growth which you can see in the picture. Any thoughts on what my plant may need? I water once a week or when soil is dry (I have not repotted since receiving) and I ensure to keep her in a very sunny corner of my living room. Any suggestions are appreciated!

You have a Phalaenopsis orchid and I am directing you to 2 places for loads of information on how to grow them.
Site 1 is the American Orchid Society's web site. Just google aos.org and below on the menu you will see "culture sheets". These are downloadable pdf files. You could download and print the one for Phalaenopsis care.
Site 2 is our Orchid Forum section here at the NGA. In those forums are numerous threads dealing with Phalaenopsis care. Pay attention to one called "Supermarket Orchids-Phalaenopsis". By reading through that thread, from beginning to end, dozens and dozens of questions are answered dealing with this topic.

Lastly I have the basics for you.
They MUST be grown in a pot with drainage holes. The decorative moss is not a good idea. It interferes with proper drainage.
Light- Phalaenopsis like a bright location such as a windowsill. NO direct sunshine. Your location seems too dull.
Temperature range of 65-80 degrees
50-60% humidity
Repot into fresh media every year or two at the most. This is needed in order to keep the roots alive. Without repotting, the roots with suffocate and die.
A Phalaenopsis is an epiphyte who grows on something for support only.
Flowers on a standard Phalaenopsis like yours typically bloom from the middle of winter through early April. Flowers last typically for 3-5 weeks each. They bloom sequentially.
Factors that shorten flower life, too much warmth, low light, too little water, a compromised root system.
Fertilize once every three or four months.

Welcome to the site!!! Check out the monthly what's in bloom thread. We are currently posting pictures of our orchids in the May 2022 thread.

BigBill- I wasn't sure about keeping that decorative moss, so thank you so much, this helps a ton!

Oh think nothing of it!
Glad to be of some help.

Meanwhile, sit down by the fire, put your slippers on and join us!! Some one will be along quickly to get the grill fired up with dogs, burgers and brats!! It is so much fun here.