Comment ça va?

You'd say 'that's a secondary issue/ problem' rather than 'a second thing'. If we're listing issues we might say 'and another thing ...' if we remember something we want to add to our list.

An English native would come from England. A Native English Speaker could come from the UK, USA, Canada or anywhere else where their first language happens to be English. If an English speaking American lived in China they'd still be a Native English Speaker. If a Chinese national living in China had an English speaking parent, they'd probably still also be a native English speaker.

As a British English speaker 'sleep', 'eye bogey' or 'sleep dust' depending on where you're from in the UK.

'On' the course, if you mean 'about' the course. We use 'on' interchangeably with 'about' on some occasions.

"Playing the Martyr" is essentially pretending to be a victim in an overly dramatic sense. You would say someone 'played the martyr' if they complained about something happening to them with the intention of making people think that they were really affected by the occurrence (when in fact they are not). 'Glass half full' is the opposite of 'glass half empty' both are sayings that suggest either a positive or negative character - when presented with a half full glass positive people will say the glass is 'half full' whereas negative people will say the glass is 'half empty' ie; one side will say the have something, and the other will say they are lacking something. A 'trying' thing is something that causes frustration or tests our patience/ character, in the same way that a 'trial' is a test physical, mentally or legally. So a year of 'trying things' would be a difficult year with lots of personal tests/ obstacles. 'Soul crushing' is upsetting/ emotionally difficult. A 'bombshell' is a big piece of (usually negative) news - so learning that you have a serious illness would be a 'bombshell'.

Better to say ' I get really sad about it sometimes.' I can't think of an example where we would say 'for it'.