You poor fucker, and no one wants to help cos it's electrical and everyone hates electrical cos it's usually an arse!!!

If you are savvy with electrical, possibly check your fuel pump's resistance across the terminals. This will tell you if there's any breakdown in the motor windings. I don't know what resistance you should expect to see. Nerds? Help please? Sure you could google it.

Tell us what pump you have too as that may affect the resistance.

If the relay is tripping, usually it's because there is too much current somewhere in the system. Alternatively, it could be a faulty, relay.

What size wires do you have, and what size fuses do you have protecting the control circuit, and the feed to the pump? These need to be right OR YOUR CAR COULD CATCH FIRE!!!

Another thing you could do is test the resistance of the circuit that goes through the boot relay. Or test the resistance between a good earth on the body of the car, and the terminals of the boot relay BUT!!! Before you do this, set your multimeter to DC Volts and test ALL the terminals to make sure you don't test between a live terminal and the car body, which will short your multimeter.

If you don't know what you're doing, get an auto sparky. They are cheap when you consider the time they save, the inconvenience of your car cutting out, and for peace of mind. They have diagnostics and experience.

Tell us the spec of your car too. Might be the pump is maxxing out or something...HATE these bloody problems haha, but you will get it fixed, so try to keep smiling