Question: When asking around, I've never heard anyone agree that a young, healthy person should end their life by suicide. But I also don't know what reason there is for that consensus. 

Did Buddha teach anything regarding what makes life worth living?

Answer: 
You shouldn't even think about things like suicide. Thoughts will be full of negative emotions and states that it will drag you to lower planes. 

When you are doing the act you will have negative thoughts which would mean that your next life is bad.

You are also breaking the precept of not killing which is very grave. 

Also it is best you see a doctor but until then practice Metta to your self and others.
This [Scientific American article](http://www.scientificamerican.com/article/is-mindfulness-good-medicine/) describes some of the benefits of mindfulness:

> 
> As a remedy for depression and anxiety, mindfulness meditation may
>  help patients let go of negative thoughts instead of obsessing over
>  them. Training people to experience the present, rather than reviewing
>  the past or contemplating the future, may help keep the mind out of a
>  depressive or anxious loop.
> 
> 
> 

If you have thoughts that are repeating in a loop, perhaps you are focusing on those thoughts, intentionally or unintentionally, and as suggested above mindfulness meditation may be a solution.

You may read [A Guided Meditation](http://www.accesstoinsight.org/lib/authors/thanissaro/guided.html) by Thanissaro Bhikkhu to understand how to practise mindfulness meditation. If [The Five Hindrances](http://en.wikipedia.org/wiki/Five_hindrances) to practice disturb you, you can find the antidotes in [this essay](http://www.budsas.org/ebud/ebmed051.htm) by Ajahn Brahmavamso.

**What is the purpose of life? Well, the purpose of life is to experience true happiness.** That's one way to look at it. From the Thanissaro essay:

> 
> Then bring your thoughts back to the present. **If you want true
>  happiness, you have to find it in the present**, for the past is gone
>  and the future is an uncertainty. So you have to dig down into the
>  present. What do you have right here? You've got the body, sitting
>  here and breathing. And you've got the mind, thinking and aware. So
>  bring all these things together. Think about the breath and then be
>  aware of the breath as it comes in and goes out. Keeping your thoughts
>  directed to the breath: that's mindfulness. Being aware of the breath
>  as it comes in and out: that's alertness. Keep those two aspects of
>  the mind together. If you want, you can use a meditation word to
>  strengthen your mindfulness. Try "Buddho," which means "awake." Think
>  "bud-" with the in-breath, "dho" with the out.
> 
> 
> Try to breathe as comfortably as possible. **A very concrete way of
>  learning how to provide for your own happiness in the immediate
>  present** — and at the same time, strengthening your alertness — is to
>  let yourself breathe in a way that's comfortable.
> 
> 
> 

And what to do when your negative thoughts come back over and over to disturb you? The essay continues:

> 
> **If your mind wanders off, gently bring it right back. If it wanders
>  off ten times, a hundred times, bring it back ten times, a hundred
>  times. Don't give in.** This quality is called ardency. In other words,
>  as soon as you realize that the mind has slipped away, you bring it
>  right back. You don't spend time aimlessly sniffing at the flowers,
>  looking at the sky, or listening to the birds. You've got work to do:
>  work in learning how to breathe comfortably, how to let the mind
>  settle down in a good space here in the present moment.
> 
> 
>