I've got a std front pipe and cat, you can have on long term loan if you need it, Its not much, and maybe its not needed [you reckon your zoorst is OK], but its the only spare part I've got left -- been selling them as I go -- otherwise, good luck. Don't burn your tyres though, borrow another set and get it passed, then put yours back on. It's only one mongrel's opinion that they are worn, others may not even notice.
As for the gf, you have to follow your own destiny and rely on your own sense of values, nobody can make your mind up for you. What you, you and your gf, do is your decision.
The cancer, I hope results are negative, but you have support and well wishes from many here.
One day you will look back on this, and it may well be a defining moment in your life, [now the feel good stuff ends] don't f##k it up.......................lol.
Everybody has a 'crunch time' at least once in their lives, some of us have been there and done that, we can sympathise.
Kick back, don't be too hasty, wait till the whole chapter is written, things will be easier.