How to make this academic year the "final year" of your PhD if your adviser does not care about your graduation and just wants you to keep working for him.

You need motivation!
Well, you have just given motivation to many by your statement "...aiming to finish quickly", because hundreds of students dream of the day when they can be in your situation...

It is absolutely worth a try if you think you are interested or you might be interested in it.
But remember to be VERY careful in choosing your adviser, because PhD is a long commitment.

CONGRATULATIONS!!
By posting this message, you have helped hundreds or more grad students by reinforcing their hope that they will also graduate one day !

It is very common to feel isolated in grad school. What you can do is talk to your adviser and make a plan about your expected graduation date. Some advisers are mean and don't agree on that. But it is very important to do so, in particular in situations where student is too lonely, because it gives you an assurance that you will be done by a particular time if you work hard.

Bullying is very common in research world. DO NOT TOLERATE IT.
A lot of bullies feed on the respect that you give them. Stop respecting them.

Crystallography is a great field. You may find it exciting to be able to measure the structures of biologically relevant systems that you may be interested in, so your background of molecular biology should be helpful. It will be a great combination of being able to measure the systems that you understand too. I don't know if you will be using x-rays for your crystallography studies?
Whether or not you "enjoy" the field will depend a lot on your adviser. Meanness, hypocrisy, etc. are some common traits found in advisers...

I will say go ahead if you have an offer from "a really nice supervisor" !