Inbound - of you put half the energy you're expending on this feckless sniveller (thanks, @Rangoon) into yourself, you'd be a new women in a few months.
The question you need to be asking yourself isn't "how do I make myself realise this guy's no good?"
It's "how on earth did I ever consider allowing this loser to even touch the hem of my robe?"
Ditching him should be pretty simple. You don't owe him anything more than a text. Short, firm, & then BLOCK. "Dear Feckless, this isn't working for me, I need to focus on myself & my career so I'm finishing the relationship but wish you well in the future" - then TOTALLY DISENGAGE.
Then find yourself a decent therapist.
Talk to them about your self esteem, about your family background & what you learned about relationships as a youngster.
Engage with yourself - stay single, really learn about what early lessons you may have absorbed that might use some unlearning. About how to put yourself first - how to be your own champion.
Spend some time thinking about what you want from life (excluding men, for a year maybe), what makes you excited, what your passions are, how you want your working life to pan out.
Then buckle up & live that life!
You are 25. TWENTY FIVE! You have decades of experience to gain, & the best footing you can give yourself is an education in what makes you tick. What causes you to self-sabotage with Mr Feckless. What made you feel this is all you are worth. What keeps you hanging on instead of embracing your independence.
Once you know yourself, your strengths & failings - such as why you accepted this nightmare of a young man - you will have the building blocks you need to make a genuinely fulfilling life for yourself. At some point, a decent man will enter that life, & share it with you. The better you can make your life ahead of that, the better your chances are for attracting & making a successful partnership with your optimum man.
You didn't fall in with Mr Feckless on a whim.
If you had, you could finish it on a whim.
The fact that your head & your heart are at war over this, to the point that you - arrrrghhh! - worry that he'll meet someone else, & are finding it so hard to just end it already, shows you what you need to do next - get some therapy.
Without it, how are you going to truly understand yourself, & stop yourself from falling for the next user & abuser?
OP - you said it yourself - this guy is no good for you. You know it. So YOU start being good for you! Find yourself an excellent therapist & start investing in the rest of your life.