In the first two lines you address the the person who I assume the poem is about. In the second you reference a third party and you ruin the flow between yourself and the 'you' of the poem. It makes it feel less personal also. If you only wanted to reference the 'you' the poem is about, just change the second line, to 'ask of me instead'. Much more personal, much more heartfelt. No third party intruding on the relationship. Alternatively, change the 'you' in the first line to [pronoun].
The comma after 'instead', on the second line, reads better if removed - so it flows straight into the question - or replaced with a colon.
Could most likely remove the comma after 'sun' in the second line, flows into the explanation better without it. It doesn't read right with the comma, and I think what you mean to say you say better without it.
The fourth line: Don't know if it's a typo or choice for the sake of tempo, but you need to at least put 'it' after sun. You can't end the sentence on 'seen', because it simply doesn't read right. Poetic license or not:
'Explain the sun to one who has never seen',
simple doesn't make sense, and it doesn't read well at all.
Really, really adore that line 'I am but a beggar for your light'. Super good reinforcement of the sun metaphor. Really good end to the stanza.
There's a change in narrative between the two stanza's so think about breaking it up just a touch further. I know that isn't good advice because it's difficult to do. Something simple like an asterisk between them, just to signify a break. Otherwise a reader might confuse the narrative for continuing and then they might not understand. You go from a very warm and loving description to an isolated tone that's fairly melancholic (especially when compared to the first stanza).
The first line 'Come again, Summer, hold me,' I'm not feeling those comma's. Experiment with how it reads when you remove those comma's, and see what you like. You can really reinforce the right mood, depending on what you want it to say.
The rest of the poem seems absolutely fine to me. As with the last line in the first stanza, I really like the line 'will my winter never end?' Really good imagery captured there. Captured throughout and reinforced there, as well.
As always I like confirmation that this feedback has been useful or not. If not I won't count it as a source to posting my own poetry for feedback. I won't your confirmation the feedback is good enough before doing that, so please let me know =]