I didn't want to ask for help because it is a very spoilerish fight, and I didn't want to spoil anyone, besides the one here were generally under-leveled and there was actually a really low chance of finding someone able and willing to help who wouldn't be spoiled. And my friends aren't gamers (unless you count card games?^^), so it was not an option.
Thanks for the link.
I finally managed to get through it by myself. I had good equipment and used stims. The issue was more of having to use a companion i didn't use usually and as of all bosses, it was all about the interrupts. And with the interface which I struggle with, by the time I clicked to my companion to heal it and came back to the boss, well, the boss had been healing itself and, well I started panicking because I needed the healing too and everything turned so wrong...
So I focused on me and I finally managed to killed it, but it is a really close fight. One bad interrupt and you're dead.
Good to know that you can actually move on to the next planet without it bugging anything, I might do that if it happens again.