At 4 months its too intense. Its stressfull balancing someone elses heartbeat on your own ribcage. - Maybe you should admit to yourself if his behaviour is sufforcating to you. And be honest about that with him. - You dont have to asume all the emotional labour he is dumping on you. You dont have to agree to this nonsense. If he wants to declare you his reason d'etre, you can say; I dont feel the same way. I can, and would live a good life, without you in it. Then look at him and say; Everytime you make such declarations, you remind me how we are not even remotely in the same place emotionally when it comes to the two of us. Please stop it, as it makes me feel uncomfortable about us being together.

He wont respond well to this. You drawing any kind of boundary will be regarded by him as a rejection of him. This is why its a problem. You should have the space for healthy boundaries, but his behaviour makes it impossible for you to have them, without doing battle with his idea of what rejection is.

Gluck ..

Ps... run.