If you consider that:
- The instrument is not worth a proper (i.e. expensive) repair
- You cannot afford a repair or a new instrument (at least for now)
- You really need to continue your practice
- You can tolerate some degradation of the sound
- You don't intend to sell it
- You don't intend to perform before a picky auditory
- You don't say who gave you this advice
(all of the above)
... you can use some glue and 3-4 small (less than 2mm wide) screws for wood to fix the neck to the bottom.
Remove the strings first.
And clean as much as practical of the old glue before removing the strings (after removing the strings, the gap will probably close).
(At minus 10 degrees Celsius guitars break in similar way, guess where I know from...)
Yes, the two problems (fingerboard away from strings, bent towards the box and the neck unglued from the bottom) are pretty much related. The tension of the strings should be counteracted by the adhesion between the neck and the box. The the whole instrument should have a characteristic posture. Adhesion obviously failed and now the neck is at an improper angle in regards to the box, the whole instrument is bent.
The wood and the glue strength both depend on temperature and humidity, but the string tension depends on humidity and temperature, too.
Strings made of natural materials (the more expensive ones in most markets, not sure in Mumbay) somewhat self-tense when subjected to humid environment. This may move the pitch up as well as break not-very-healthy instrument like yours.
Strings made of artificial polymers (nylon, etc...) are more or less insensitive to humidity.
p.s.2 ...and I think "harder" and "softer" strings for violin do exist (but I am not a violinist and don't know for sure). "Softer" varieties should require less tension for a proper tuning.
Your questions hint that you are not very much used to simple mechanics and woodwork. If you choose to repair the instrument yourself, it is good to get a help from someone at least somewhat experienced in carpentry.