Four short lines carry a surprising amount of ache. The title tells us the speaker is an old drunk, and "Lit again" works on two levels: he is drunk once more, but the phrase also suggests something switched on, as if a lamp or a cigarette had been lit. Either way, it sounds like a habit repeating itself.
The second half turns to someone else. The speaker imagines that if his absence were "with her," meaning perhaps that his missing self could stay beside her, then he could "carry [his] age." The wording is oddly tangled, and that seems to be the point. The poem suggests he feels his years as a burden, and that being apart from this woman, or being a lost presence in her life, is part of what weighs on him. The mood is quiet, rueful, and a little self-lacerating. There is no big confession, just a tired man admitting how much lighter life might feel with her.