Your poem does a good job at avoiding being cliche, while still managing to utilize powerful words. I feel that  the following may need some revising for flow:

Hung up

on things that never were,

on no life

I could ever live.

 

 

My only support gone

forever.

Maybe take out "forever", or express the sentiment in a less deadpan way.  Overall though, good stuff.

Good job! Just a few things to say:

12:21 AM I look down upon a busy city. Anonymous. Alone.

You probably didn't mean this, but if you did, fantastic: 12:21 AM is at the same time an obscure and unified time, 12:00 being a time that can become confusing when one is not paying attention to detail (night, morning or afternoon? one day or another?) and 21 minutes after a time being a random assignment of numbers. It becomes unified in that 12:21 is a palindrome, thus a special time like 11:11 or 124. All of this relates the the persona: Anonymous, but important enough for the reader to be spending time on.

My chic apartment is empty echoing the sounds of lifelessness.

In any other setting I would have red-penned the word "chic" since I hate it completely, but here it sounds delightfully foreign and I let it rest where it is. The use of the words "echoing" and "lifelessness" in the same sentence has an amazing effect. Again, it probably wasn't your intention, but "lifelessness" repeats ("echoes") the "ess" sound. Maybe you have some sort of subconscious poet-channeling ability. Or maybe I'm not giving you enough credit, because the rest of the poem's language devices indicate that you are cognizant of your use of devices.

I was prepared to tie the knot. But she refused, afraid a ring would choke her youth. Now I’m tied to nothing but an empty room, an empty life. My world pulled out from under me.

This is where I was filled with childlike glee. This is the first time I've seen this kind of effective foreshadowing on a website meant for unprofessional writers. These lines and the following are incredibly effective, really amazingly pulled off, and I'm really happy that you could manage to create this type of imagery.

Hung up on things that never were, on no life I could ever live. My only support gone forever. She has left me here to swing…

Again, "hung up", marvelous. "My only support gone forever," same story. At "She has left me here to swing", the reader flips out with "I knew it, I knew it!" You have done a wonderful job here of showing and not telling. Nowhere did you say, "So I hung myself, because, whatever, y'know?". No, you have done your duty as the poet to let the persona say what is necessary and let it all fall where it may. Incredibly well done, I am truly impressed.