tāb-e ʿishq nahīñ hai dil ko jī bhī be-t̤āqat hai ab
yaʿnī safar hai dūr kā āge aur apnī ruḳhṣat hai ab
1) the heart doesn't have the strength for passion; even/also the inner-self is strengthless now
2) that is, before me is a long-distance journey, and it's my leave-taking now
In the present verse there's no mention of the difficulty or the pain of passion. Simply the experience of passion, in itself, is fatal. In passion, life becomes more intense than usual. The elders have called it overheating to the mind, and have gone beyond this to call it a defect of the mind, because in it man's relationship to the commonplace realities of everyday life remains greatly diminished.
ʿishq ik mīr bhārī patthar hai
kab yih tujh nā-tavāñ se uṭhthā hai
[passion, Mir, is a singularly heavy stone
how could it be lifted by strengthless you?!]
But when passion has taken hold, there's no escaping it. On the other hand, the courage for living an ordinary life has also diminished, because the inner-self has been called 'strengthless'. But the lifetime nevertheless has to be made to pass, and has to pass. In order to explicate this reality, Mir chooses as a metaphor the kind of traveler who has to make a long-distance journey, and who doesn't have the courage for such a journey, but who also has no choice but to take his leave and set out at once.
In order to judge of the mental state of such an individual, also keep in mind that in Mir's time travel wasn't easy; the road from Delhi to Lucknow was traversed in thirty days. Up to Ghalib's time, the journey from Delhi to Rampur took seven days. And these journeys were made in ordinary circumstances and in a state of good health. In the present verse, the traveler's life is in danger, and yet it's necessary for him to undertake the long journey at once.