all being one thought of you ; (line 7)
The speaker eventually merges himself completely into one big ball of thought about the woman. Love is often thought to be the merging of two souls, and the speaker reenacts this process in his mind.
Or in a thousand more, forgot that too. (line 8)
Wait, so let us get this straight: the speaker has become so wrapped up in mourning his lover's absence that he…forgets about his lover? Maybe the point is that his mind has become a total blank, an emptiness, because she is not there to fill it.