T.S. Eliot--The Love Song of J.Alfred Prufrock

The poem starts out by the narrators imagination of how things could be with his lover. I think that he is in love, but the woman doesn't respond with the same feelings. Also, I get the impression that the man doesn't have the courage to confess his love because he doubts himself in many instances. For example, in lines 38 and 39 he says

To wonder, “Do I dare?” and, “Do I dare?”
Time to turn back and descend the stair,

. Also I think that he holds himself back because he doesn't feel worthy of his love, as described in lines 40-45. I also think that he describes his past "loves" and compares them to the one he has present and finds no comparison because his present love is like no other.
I don't really understand the lines in between 100-110, maybe they are more background details??? 
Towards the end again he brings up the fact that he is getting older and may never have the chance to be with his love. The lines that I found saddening were line 124 and 125 where he says: 

I have heard the mermaids singing, each to each.
I do not think that they will sing to me.

Eliot's poems seem very depressing and full of mixed emotions and they are pretty tough to understand!