is my assassin always gonna need help with mq?

MQ will always be challenging for an assassin. You don't really have sustaining abilities, and your health/mp is low, so drawn out fights are bad for you. You aren't really useful at all really until much higher level. 

however, sins and any other class can solo mq if you do research about the best way to survive boss battles and such. If you build to have extremely high evasion and decent health, you can use poison to get through quite a few bosses. You can try to spam backstab and die over and over. Since backstab damage is so high compared to other skills, it actually works sometimes. Even with like 8 deaths and waiting for pet heal every single time, you might be able to kill the boss before the timer. However, if you don't want to reset or repurchase gear, you will have a much harder time soloing mq. 

A pet is necessary for a sin to solo mq bosses. You can keep your build and buy a decent pair of claws to do double damage if you want to use agi or if your gear isn't too great. 
If you are talking about MQ in general and not a full solo, then I would say get a Veltria. It will help heal anyone who is tanking or helping to kill bosses, because mq bosses in a party are of higher difficulty than a solo. 

A good strategy I recommend is using poison, and ranged weapon of some sort (usually a throw because you use them anyway). Poison it and run like a wizard would while draining. Once you reach level 260, you will have access to venom fist, which will make this poison strategy much more effective.