thanks for the comments.

So I had some therapy (CBT) a couple of years back and have also been on medication prescribed by a psychiatrist since.
The therapy started out well and I definitely saw some benefits. However, as we went into these 2 specific relationships the therapist started suggesting that I wasn't being caring enough for my wife's feelings and that maybe I wanted a physical relationship with my sister in law. I didn't go back after that session as it just proved that nobody gets what I feel. I spiralled downwards from there until I reached a day where I had everything planned and accounted for so that my wife would be cared for and notified in a safe and caring manner of my suicide and would be provided for in the future. Obviously I didn't go through with it in the end and I just carried on pretending things were ok. As so often happens day by day, little by little, things get a little better. But, the problems that are at the root don’t go away, so I’m back in the same situation not knowing what to do.
My health insurance deemed my depression as chronic and will therefore not cover any more therapy and my psychiatrist has retired, I can’t afford to pay for more therapy and the waiting list for public help is 8 months.