It may be argued that according to Manu samhita divorce is sometimes allowed. So why did Srila Prabhupada stress to his disciples about sticking together? That's because a Vaisnava knows that this human form of life is not meant to be wasted in the pursuit of sense gratification.
"Refraining from sensual enjoyment, one should voluntarily accept all sorts of difficulties for spiritual realization. This is called tapasya. An enjoyer of the senses can never realize God, godliness or the science of theistic knowledge."--CC Adi 1.50p
Thus Prabhupada's message to us was always urgent. Don't waste time trying to find or expect that perfect husband or wife. Krishna consciousness is the greatest emergency, the greatest need. This was Srila Prabhupada's mood. Any advice beyond that principle is for karmis. Fix the heart upon getting Krishna instead. We can make this our last life in this material world by accepting whatever is our lot, doing our material duties as far as we must, but in the meantime doing all that we can to execute the real purpose of life:
"By material means, one cannot avoid the happiness and distress unique to his particular body. There are 8,400,000 bodily forms, each destined to enjoy and suffer a certain amount of happiness and distress. This we cannot change, for the happiness and distress are ordained by the Supreme Personality of Godhead, in accordance with whose decision we have received our bodies. Since we cannot avoid the plan of the Supreme Godhead, we must agree to be directed by Him, just as a blind man is led by a person who has eyes. Under any circumstances, if we remain in the condition allotted to us by the Supreme Lord and follow His instructions, we will become perfect. The main purpose of life is to follow the instructions of the Supreme Personality of Godhead. It is such instructions that constitute one's religion or occupational duty...
"The analogy (was given) of bulls moving under the direction of the driver of a bullock cart. The bulls, being completely surrendered to the driver, remain wherever he wants to place them and eat whatever he wants them to eat. Similarly, being completely surrendered to the Supreme Personality of Godhead, we should not aspire for happiness, or regret distress; we must be satisfied with the position allotted to us by the Lord. We should follow the path of devotional service and not be dissatisfied with the happiness and distress He has given...
"'In this age of Kali, there is no other way, no other way, no other way for spiritual perfection than the holy name, the holy name, the holy name of the Lord.' Everyone should be given the chance to hear the holy names of the Supreme Personality of Godhead, for thus one will gradually come to understand his real position in life and be elevated to the transcendental position above the mode of goodness. Thus all impediments to his progress will be cut to pieces. In conclusion, therefore, we must be satisfied in whatever position we have been put into by the Supreme Personality of Godhead, and we should try to engage ourselves in His devotional service. Then our lives will be successful."--SB 5.1.15p
A revered Vaisnava sannyasi, whom I admire very much, once commented that if he were to write a book about marriage he'd simply write, "No divorce", "No divorce", "No divorce", on every page. I appreciated his statement, but later I decided that if I were to write a book about marriage it would state the most imperative, "Become Krishna conscious!", "Become Krishna conscious!", "Become Krishna conscious!", on every page. Better yet, it would read, "Chant Hare Krishna!", "Chant Hare Krishna!", "Chant Hare Krishna!", since the superior taste for Krsna's holy name defeats all material desires in comparison. Krsna consciousness and chanting Hare Krsna is so nice that one automatically becomes willing to tolerate so many difficulties in order to continue uninterrupted.
"Unless one is able to relish happiness from within, how can one retire from the external engagements meant for deriving superficial happiness? A liberated person enjoys happiness by factual experience. He can, therefore, sit silently at any place and enjoy the activities of life from within. Such a liberated person no longer desires external material happiness. This state is called brahma-bhüta, attaining which one is assured of going back to Godhead, back to home." Bg5.25p
Otherwise, our effort to counteract material distress, in truth, perpetuates our material existence (SB7.9.17). I knew a lady who was married to her fifth husband. Here's her conclusion she revealed to me: "I should have stayed with the first." She realized that as long as our hearts remain impure, we will never feel satisfied. Unless we learn to tolerate via a higher taste, we will be forced by the laws of nature to seek out another partner (and sometimes even another, and another) or other means for sensual gratification. Superficial renunciation cannot last (Bg 18.8).
Keeping this in mind, marriage is seen in its proper perspective. It becomes a steppingstone toward actual self fulfillment rather than a goal. "All occupational engagements are certainly meant for ultimate liberation. They should never be performed for material gain. Furthermore, according to sages, one who is engaged in the ultimate occupational service should never use material gain to cultivate sense gratification. Life's desires should never be directed toward sense gratification. One should desire only a healthy life, or self-preservation, since a human being is meant for inquiry about the Absolute Truth. Nothing else should be the goal of one's works." -SB 1.2.9-10
This path of tapasya for the sake of spiritual progress cannot be appreciated by those addicted to sense enjoyment and material achievement. The Bhagavad gita calls such persons less intelligent, because even if one has the best case scenario possible in this world, that happiness is temporary (Bg 5.22), and as long as the heart remains impure, one's so called "love" for husband and family is really just a business arrangement which can terminate as soon as the other party fails to match one's expectations.
"According to Bhägavata philosophy, every human being is meant simply for this tapa and for no other business, because by penance only can one realize his self; and self-realization, not sense gratification, is the business of human life. This tapa, or penance, was begun from the very beginning of the creation, and it was first adopted by the supreme spiritual master, Lord Brahmä. By tapasya only can one get the profit of human life, and not by a polished civilization of animal life. The animal does not know anything except sense gratification in the jurisdiction of eat, drink, be merry and enjoy. But the human being is made to undergo tapasya for going back to Godhead, back home." SB 2.9.6p