How might one paraphrase and explain the meaning of the second stanza of Richard Lovelace's poem "To Althea, from Prison"?
The second stanza of Richard Lovelace’s poem “To Althea, from Prison” reads as follows:
When flowing Cups run swiftly round
With no allaying Thames, 
Our careless heads with Roses bound,
Our hearts with Loyal Flames;
When thirsty grief in Wine we steep,
When Healths and draughts go free,
Fishes that tipple in the Deep 
Know no such Liberty.
These lines might be paraphrased and analyzed as follows: when cups of wine, freely filled and refilled, are passed around and consumed and when that wine is not diluted either in flavor or in alcoholic content by having water from the River Thames (the main river in London) mixed with it; and when we wear crowns of roses on our heads (heads which are free from cares); and when we feel in our hearts the fire of loyalty (probably loyalty to King Charles I, who was in conflict with Parliament at the time this poem was written, although “loyal” here may also imply loyalty to one’s friends); and when we drown our sorrows by drinking wine; and when we are free to drink abundantly to the health of others and propose toasts to their health as we do so drink; when all these events occur, then the very fish that drink from the sea are not as free as we feel, even if we are imprisoned.
This stanza seems to imply either (1) drinking with fellow prisoners; or (2) drinking with friends who visit the speaker in prison; or (3) both. Such visits were not uncommon.
The first stanza of the poem had emphasized the consolations that feminine beauty could provide to the imprisoned speaker. This stanza implies that consolations that can be provided by (probably) male friends and fellowship and by shared drinking. In both this stanza and the first stanza, the speaker implies that although he may be imprisoned physically, in his mind and soul and spirit he is essentially free. In other words, he responds to his predicament with a kind of Christian stoicism. The Christian flavor of his response will become clearer and clearer as the poem proceeds.