Our speaker is a very lonely man (we're assuming he's a man), there's no doubt about it. In the first two lines the speaker tells us that nobody cares about him, or even knows who is anymore, and that his friends have pretty much abandoned him. He might as well be non-existent, like "vapours." Throw in the fact that there are no "joys" (9) and that everything he once loved is one "vast shipwreck" and you have a picture of almost total misery.
Now some of this misery might just be because the speaker's friends are being total jerks, and some of it might be because he's getting older. After all, life starts to look a bit different as we get older: people move away, people die, people change. Either way, this misery gives our speaker a death wish. But he's not suicidal or anything like (he doesn't say anything about killing himself), even though his mind may be going (things seems "strange").
Last and certainly not least, he's kind of a religious or spiritual dude. He's not really afraid of death because he's confident that he will meet God, his creator. You certainly wouldn't hear that from an atheist now, would you? Like a lot of people who believe in God, our speaker sees death as a peaceful sleep, an escape from the troubles of life. Well at least he's not super-scared or anything like that.
A few last words before we let you go. Technically speaking, the speaker and John Clare aren't the same person. Poets write poems, but it's not always them talking. "I Am" is a strange little exception to this general rule. Okay, yes it's not Clare, but in a way it kind of is. Clare was a very lonely man later in life, and his family never visited him in the asylum. Plus he went crazy, which is why he was in the asylum to begin with, and he was a pretty pious dude (see the religious part above). So, in this poem the speaker is and isn't Clare. Try that one on your friends and watch them admire your literary sophistication!