Hi there welcome to just answer hope i can be of some assistance to your problem if you connect a jump pack up to your vehicle and then try and start it does it improve the situation.
sorry forgot to ask as well how does the engine turn over does it sound slower than it use to?
Have you had your starter motor checked?
Yes this is why i am asking as i have seen this many a time before, now what happens it the starter motor becomes lazy and then it requires more current from the battery to rotate it, this then causes the battery voltage to drop below 10volts and once this happens the modules on the vehicle shut down hence it does not start.
There are two ways of testing this to confirm this problem, you can either connect a jump pack and see how it starts if it starts ok then i would suspect that your starter is at fault.
Another way of testing this is by using an amp meter now you may not have one of these as it is normally electrians like my self that have these but if you do then you can measure how much current the starter motor is pulling when cranking you would normally expect around 150- 200 amp on crank where as one that is lazy you could expect up to 500 amp which is going to really put a load on the battery.
Give this a try and see how you get on if this is ok then it is possible you may have a air ingress on the fuel system causing the fuel to drain back. if you require any further help then please ask