Question: How to stay self-motivated?
Answer: Firstly, regularly watch good box office movies in a theater and pick the best parts of the movie where Good wins over Evil. Avoid horror movies, if possible. Secondly, surround yourself with good media and positive people around. Thirdly, when down then remember how our ancestors like Satya Harishchandra, Lord Sri Rama and Pandavas suffered in past and still won their battles. Last but not the least, share your woes with your trustworthy senior people to get advice on staying self-motivated. My last piece of advice on this is, 'Nothing is permanent, so are our woes too. Never think you are alone'.
Question: Why suicide is a sin?
Answers: One faces hardships because of one's negative karma in current life/ past lives. So, if one wants to evade those hardships and commit suicide, then God will not forgive him for suicide is a sin. One will go through hardships in current/ future reincarnations until one's soul is cleansed. Suicide cannot prevent one from paying for one's negative karma. Praying to God for forgiveness and true repentance is the way towards absolving one's sins, but not suicide. Never ever think about suicide.