Thanks for the replies. i didn't see them until now. Very helpful.

Conceptually yes, probably need of love or reproduction (in the sense of getting girls). This is strong enough to generate some violent states of mind.

As i said they are very invasive and tend to persist because they are triggered also by sensory inputs that are always there, such as pain, proprioception and chemicals in the chest, throat etc.
So i was thinking about leaving completely the practice of focusing on the abdomen, and instead cultivating awareness of the feelings (emotional) that arise. That would mean abandoning the practice of Samatha, wouldn't it?

The problem is that if i continue to try to be focused on the movement of the abdoment without losing it in distraction.... i cant
It is an infinite yet lacerating operation.

Another issue is whether to give a name to the states that arise or not. I think noting is good explicitly for recovering immediately from distractions, to return fast on the object of concentration. But if i don't use such an object? Also, probably i would have to note just a few things repeatedly and use a limited vocabulary.

I am confused to a high degree about what to do.
I'm trying to concentrate to the nostrils airflow as of now, sitting (i can keep my body still enough). I don't know what to do with unpleasant feelings that arise. In MCTB i'ts written that first one should begin to practice concentration on an object at least to access concentration. It is also said that the mind faculties (my term) of insight and concentration are different and can be developed independently or in combination. From this i understand that developing concentration helps the practice of insight. If i suppose that it would be great to attain access concentration first, why should i begin with something dispersive as walking meditation, that it looks like more an insight practice (from Daniel's post "paying a lot of attention to every little movement...")? Also, i tried it two days ago and done slowly it's worst that be sat. To do it someway without worry or pains it should be much faster, in the streets or some park almost at normal walking speed, but done this way it becomes hard to pay attention to every little movement.

I can't probably begin with taking pain as an object of concentration because it often isn't there at the beginning, i should begin with nostrils. It also changes place such as the back, cervical area or sometimes shoulders and it triggers a global feeling in the thorax, abdomen, stomach, throat, mouth etc. It's not the pain that is felt when, for example, you accidentally hit the nerve of your elbow. It feels like chemicals are spread trough the body, particularly in the areas listed before. Think about if you go home and find your loved one in bed with someone else (sorry for the example lol), then a strong burning-like depressive or quite unpleasant feeling would start to pervade the body, particulary the chest area wouldn't it? It is like this (just probably less intensive than the example).
So these feelings are multiple (there is also the bare physical pain) and wide, they summon thoughts, suck up energy and motivation, and are not always there. As a preliminary program i can concentrate on the breath for how much it is possible, then if they become too much a distraction putting the breath aside and start noticing the related vibes and so on. It sounds strange.

There is also the exercise of the index fingers, but can the faculty of concentration be developed too with that exercise? (as it is presented as an investigation in Impermanence). Shouldn't i begin with attaining access concentration first? Does the latter consist of noticing the vibrations that derive from JUST the object took in account, and the first in noticing all that is in the field?

I had that to say. Thanks to everyone for giving attention to my previous messages!