I don't think telling him it's over is a good idea, it would probably trigger a big emotional fallout and him trying to manipulate me to stay.
Ah, see, this is the crux of your problem. You feel a sense of compassion for and obligation to take responsibility for the drama he creates around his feelings, but the fact that he can't take deal with his own feelings in the way healthy people do is why he's emotionally abusing you in the first place. And the fact that you take too much responsibility for managing other people's feelings is how you ended up in a relationship with a manipulative fucker like this in the first place - take it from someone who has been there.
You need to understand that the breakup drama is just another form of his emotional abuse, and you are 100 percent entitled to say NO to it. It does not make you mean or cold-hearted or responsible for him throwing himself off a bridge if it comes to that. You are not his saviour from the bad feelings that arise in him when you tell him you no longer want to be with him because he lies to you, future fakes, treats you with disrespect and otherwise shows himself of being in a healthy mutual relationship. You're just not, no matter how much he insists you are.
I know it's hard to get your head around because you have a lot of empathy and would hate to be dumped and cut off, but the truth is you are dealing with a psychologically unhealthy person and you are not responsible for his wellbeing. You are responsible for one person's wellbeing and that person is YOU. The fact that he can't see his own problems is NOT YOUR PROBLEM TO SOLVE.
You are fully entitled to end the relationship if you're not happy, which you know you're not. You don't owe him a relationship. You don't owe him a relationship if he promises to change. You don't owe him a relationship if he says he can't live without you. You don't owe him a relationship because he's got mental health problems that he thinks can only be fixed by the love of a good woman. You don't owe him a relationship full stop.
My advice would be to get super-clear in your head about the reasons you want to leave. Organise to meet him somewhere that you can leave when you need to (a cafe or public place, certainly not his house or yours) and prepare a short speech, like, "Bob, I need to talk to you. I've been doing a lot of thinking and I've realised I'm not happy in our relationship, and I don't believe I ever will be. We've had a lot of issues (insert reasons if you want) that you're well aware of, and I've decided I just can't move past them. So I would like to break up. I'm sorry, I know you will be disappointed, but I have to do what is best for me."
That's it! That's literally all you have to say. If the manipulations and promises to change and accusations that you're heartless and uncaring and all the rest of it commence, keep these phrases in mind.
"I'm sorry you feel that way, but this is what I want and I'm not going to change my mind."
"I do care about you but I don't want to stay in this relationship."
"I know you feel you can change but I'm not prepared to give the relationship another try."
"I'm not going to argue with you... I've told you how I feel and I would like you to respect that."
You may have to repeat these a lot, and when you do, keep in mind that the reason you need to repeat them is his inability to accept your feelings and desires as valid – the exact problem that is is at the heart of your relationship issues. The more he goes on, it's just more evidence of his issues. Remember that he's not saying it out of love – his actions have clearly shown that he doesn't really know what love is – he's saying whatever he's saying because he can't stand not being in control of you.
If he threatens to hurt himself, you can say
"I really don't want you to do that, and if you truly feel that way I think you should contact mental health services or a friend and get some support. I'm afraid I can't give you that support though."
At the point where you feel you've had enough of the conversation, you can say, "I know you're feeling very hurt and upset right now, but I don't think continuing to talk about this is helping. I'm going to leave now. It might be a good idea to call a friend or something if you need to. I think it would be best for us both to have some space to process, so I'm not going to answer my phone for the next few days."
Then, leave. (If you think he might try to follow you, you could organise to have a friend close by to meet.) Then that's it! You're done!
Of course, he's going to try to contact you afterwards. In that case, just reiterate your need for space, and keep remembering "I am not a bad person for expecting him to deal with his own feelings." I am pretty sure that at some point he will escalate to threats and more attempts to change your mind, at which point you can say, "We've broken up, I understand it's hard and you're upset but the way you're behaving is unhealthy and disrespectful. I've told you I am not going to change my mind, and I am not prepared to continue to speak to you unless you can respect that."
If he disrespects you, block him. And spend your time reading about self-love and overcoming co-dependency. A big part of your journey will be about learning healthy ways to take care of your own emotional wellbeing and see your needs and happiness as equally important as everyone else's – and how not to assume responsibility for taking care of someone else's emotional wellbeing.