Hi,
Usually in a single vessel disease medical treatment with drugs is advised, but depending upon your individual condition stenting could have been advised. Have you got a 2D echo done recently? How is your EF? Quitting smoking or alcohol completely can bring a difference but in the long term not immediately. I would recommend that you take a second opinion and get regular follow up to monitor changes and if required stenting can be done then. Best.
70% blockage is not usually considered critical but should be monitored at the very least.
I've had a total of 8 stents in 4 different procedures, (4 coranary arteries, 4 femoral arteries) Don't be afraid of the procedure, you're usually in and out of the hospital the same day, there is little if any discomfort and you can resume normal activities in just a few days. If you have confidence in your cardioligst follow his advice, if not, get a second opinion.
Hope this helps, good luck!