99 Mustang Not starting- Gas line, electrical?

I have a 1999 Ford Mustang V6. About 4 months ago, my car wouldn't start one day. It would turn over but wouldn't start. It had done this very soon before that day but would finally cut on after a few tries, but not this time. We ended up replacing the fuel filter and it continued to work fine for about a month or so. This same instance happened again a month and a half later. On this second occurrence, we sprayed ether into the intake. It automatically started. After that, we took it again to replace the fuel filter. For the third time, my car has done this. On this most recent instance, we sprayed ether into the line again and it started working. Each time, we will change the fuel filter and/or spray ether and then it will crank and work fine for about a month or two. We have no idea what's going on and neither do any of the mechanics we've talked to. Help?