There are others better qualified to offer you advice on this, but the ball is firmly in your court.
Understand the job issues, and civvy has to take priority - the army can't pay its own bills, never mind yours.
If the work / life /TA balance is not possible, then speak to PSAO and explain it to him. A lot of people here will gripe that you've "wasted time and money" by binning it during your training. - There again, you aren't stopping somebody else from joining.
Is the new job "pressure" a short term thing or situation normal from here on out?
If the job issues are likely to be temporary, then the TA will probably be able to accomadate this. ie. pizz off for a year and come back to us.
If this is "really don't want to be part of Tony's box of soldiers anymore", then the job isn't the issue. Have you enjoyed your time in the TA so far?
If the honest reason why you want to leave is that your new job will take up too much of your time, consider transferring to a Specialist Unit.
I don't know what your job is, but it's probably included in:
Admin And Office Work
Electrical and Mechanical Engineering
Geology and Geotechnical Engineering
Ports and Railways
Power Production and Supply
Water and Sewage Treatment and Distribution
PTP's message and Goku's are both good advice. Don't be worried about speaking to them (your unit) and telling them the score. As Goku says, they need to understand why people do leave, and how they can best address this in future.
Your situation is going to become more and more common - more people, work further from home, often overseas, then ever before, the TA needs to adapt to this. By just going - which always appears a bit suss, they don't get to hear your side of it, which doesn't give them the opportunity to help you or offer alternatives.
Good luck with BA - I guess this isn't the place to discuss your crucifix!