this poem is awesome, like how you get into another persons perspective. i think you should remove all the commas at the end of the lines because they serve no purpose. 

peace

I agree with the critique above in that you should drop the commas after every line.  It makes the whole thing feel like an extremely long run-on sentence when instead there should be stops and pauses to divide ideas and accentuate certain feelings and moods.  In fact I think it's pretty hard to read as it is because I find the commas so distracting.

Some more specific critiques:

I thought my old mind would serve me well, And I’d lose you with the rest of my memory,

I see what you're getting at here, that losing her memory would be his mind serving him well.  But I think the phrasing is a bit awkward, because reading that first line, you're expecting to read about his old mind still being sharp.  The next line contradicts that, and I understand what you're getting at, but I think it could be phrased to use a less common turn of phrase that doesn't evoke any expectations.

I fear the only cure for this wound, Will be the Earth’s sweet embrace,

You use two overused phrases here, "I fear" and "sweet embrace," which besides being cliched don't really fit with the voice of the poem so far.

But if my soul is to go on forever; never to know an end,

The semicolon here is misplaced.  It should be a comma.

But when you died my soul lost love like blood, Ever since empty eyes have slowly seen it bleed,

I'm not sure where you're going with the empty eyes image.  Whose empty eyes?  Also, by saying "ever since," you imply the simple past tense, but you use the past perfect (I think that's the one) tense in "have seen", which doesn't match.

Behind my glass; watch the world go past,

Again, no semicolon, but it's hard to tell because of all the commas at the end of the lines.  It's possible that a semicolon would fit here, but without a full sentence as context, it's hard to say.

Falling into the unknown while I fell inside my own head,

I think this would sound better as "into" instead of "inside"

I'll be honest when I say I think this poem needs a lot of work.  The first step would be adding real punctuation.  Next, I think you should work on some of your vocabulary.  I can't put my finger on it, but I felt like a lot of the lines had a stilted feeling.  I couldn't imagine anybody having an inner monologue that sounds like the lines in this poem, especially a depressed, grieving widower.  Something about them just doesn't ring genuine.  But this may just be a symptom of the punctuation.

I also had difficulty connecting emotionally with the speaker.  I'm going to be blunt when I say that this kind of poetry, that is, poetry focusing on depression, loss, loneliness, and sadness, is sometimes the easiest to write, and consequently the hardest to connect to.  We all have these feelings, and it's certain that your poem has some meaning to you personally; but as a reader, I finished reading and found myself without any emotional response.   Why should we care about this widower?  Everybody's lonely sometimes, and there's millions of other widowers out there who feel just like he's feeling.  Why is he special?  Why are we listening to his inner monologue?  After reading so many other poems about how sad the speaker is, and how deeply lonely they are, and how they want to die, and so on and so on, one gets desensitized.  You've got to really give the reader a reason to forget their own problems and care about the speakers'. 

I guess what I'm trying to say is, putting some words down about how lonely the speaker is is a far cry from actually making those words register with the reader.  That's the hard part and what I think needs to be worked on most in this poem.

Sorry if this critique comes across as a little harsh, but I really want to see this poem improved.  Hopefully you'll find some of this advice helpful!

I thought my old mind would serve me well,

And I’d lose you with the rest of my memory,

The first stanza had a great flow and set the theme up well.  Here, the flow stopped, mostly because of words that seem to stumble.  I think, perhaps, it's the use of unnecessary words, like 'old'.  Actually, I think that's it.  Without them, "I thought my mind would serve me well.  The next line just doesn't flow right.  Something with the wording.

But when you died my soul lost love like blood,

Ever since empty eyes have slowly seen it bleed,

Now these two lines are great.  Nice flow, great imagery.

Will be the Earth’s sweet embrace,

I think the word sweet, though it's something to look forward too, doesn't fit into the tone of this poem. 

Your Heaven seems like something that can never come,

Lies they tell old men until their ears can hear no more,

But if my soul is to go on forever; never to know an end,

Why won’t someone tell me just what I’m heading toward?

 

Here, again, the flow just is interupted with a lot of words.  Most of this poem is quick, to the point phrases, and here you break into long sentences. 

Though my reason to live it has already gone?

Here, I'd remove the words 'to live it'.  It still makes sense and takes down on the wordiness.

Is it weakness to give into the fatigue I feel,

You could take off the words 'I feel', getting more of a bang for your buck.

It was courage when she was forced to close her eyes,

Falling into the unknown while I fell inside my own head,

But what does debating character and cowardice now gain,

When I don’t even have the courage to get out of my own bed.

Again, another stanza of long sentences with too many words in a poem with short phrases. 

Overall, you handled the theme wonderfully, and you have a real sense of words.  You can certainly turn a mean phrase.  The only real problem I have is flow and wordiness when it's unnecessary or doesn't fit. 

Thanks for the read.

I really enjoyed the way that this was written. That being said, I think you aught to explore new vocabulary to expand your range. Some words just fit better, y'know? Other than that, your poem is very emotive and interesting.