Description: Whoop-de-doo, another love poem. I said I wouldn't write any more of these.
I honestly don't know where this poem came from.
"Tenderer" isn't actually a word but I don't care. "More tender" sounds awful and makes the poem taste like burnt macaroni.
Bluebeard's Love Poem -------------------------------------------
This great longing, this,
as full of force as the wind;
it throws daggers against my inside,
than you know.
I will take her to be mine.
We will wed in the winter;
the snow is pure and it
can be trusted.
I will take her heart and
lock it in a small stone box
so it cannot betray me;
I will bury her smile in the deep and lonely woods
so it can smile for no other.
Bluebeard would adore your selfish sentiments regarding locking up love so that it would remain forever faithful. Of course, he would need to meet a masochist worthy of such entrapment (or at least willing to be entrapped).
My vote is for "more tender" rather than for "tenderer," but that call is yours to make.
I like the honest character behind this poem. It's not all I can see is you, because the narrator can see other people and he doesn't want them to touch her! For me, in reading this poem, it sounds like this lady-friend may not know the narrator too well at all. He has all these dreams of him and her together, and is very protective -- somewhat paranoid -- of somebody else getting into the mix. Somebody might already be in the mix and he doesn't know what to do because he feels so strongly about her. That's how I'd read it anyway.
I need to agree with Azura and C.L. though; I think the 'tenderer' doesn't quite work. Now that may only be because you have mentioned it and these two have also commented on it, but with some consideration I would much prefer to read a 'more tender'. The childlikeness that Azura mentioned is not necessarily a bad thing though. From the way I interpreted the character, I see him as very childlike, especially with his not trusting anyone. I would argue that it doesn't fit rhythmically; that it distracts somewhat from the flow. The current, 'tenderer', has a strong syllable and two weak ones whereas the debated, 'more tender', in this context, can be swayed into a weak/strong/weak syllable reading. I think that it sounds better like that, not that you're conforming to any rules by doing that but that it gives a better feel of euphony. Also, 'more tender' may have a certain feel for you but many others may not stumble on it at all -- and vice versa. I suppose you know what you want it to sound like, but a good thing to do is to write down pros and cons on each side.
In the fourth line, 'which is', you use the singular verb 'is'. This would make sense if you were referring to a singular tender act of throwing daggers, but would not fit so if you were referring to multiple tender daggers. Just to clarify, 'is' would refer to the act and 'are' would refer to the daggers. I suppose 'is' could refer to the 'great longing' but this is more obscure. The reason I mention this is because I stumbled a little when I read 'is'! No worries though. I think it would make more sense with an 'are' and therefore be referring to the daggers.
Overall, this narrator seems quite selfish, as all acts of love mentioned would benefit himself by oppressing his beloved. I think the character is constructed well and the poem does an honest job portraying a different side of love. The line breaks are not obstructive and flow quite nicely too. Good job!