In MY opinion, it is not a sin, but it is a permanent solution to a temporary problem.
Things MIGHT get better.
As some old pagan said, more than a century before whatever dates are given for the birth of Jesus:
"It is not what OCCURS, but how we CHOOSE to FEEL about it, which determines whether or not we are happy."
Back in the EARLY days of Christianity, life in general was even crappier than it is now.
You wouldn't get sick, and run up enormous medical bills to get cured.
You'd get sick and DIE.
And nobody knew about germs.
They were very sure that diseases were caused by rampaging demons, or inflicted by a vengeful GOD.
And along came Christianity, telling people tat, instead of living a life of hard work and constant discomfort, they could be in Heaven, surrounded by LOVE and perfect happiness.
Christians were killing themselves, a LOT.
Including very sincere Christian priests.
Hey! Without preachers spreading the word, and without people in the pews dropping coins into the plate, the Church was not able to turn a profit.
So, guys like Thomas Aquinas and Augustine of Hippo came up with theological explanations as to why suicide MUST be wrong.
And because the Church and the ruling class were real good buddies back then, the secular laws were passed, making it a crime as well as a sin.
So, rather than avoid suicide because it's a SIN in the Christian church, do what the ancient PAGAN suggested.
Adjust your attitude so that the shlt that makes you unhappy, does not make you THAT unhappy any more.
Choose to NOT feel unhappy.