Is it helpful to stay single if I am not going to become a monk?

Maybe you can try to guard your sense doors. This can be the best help you can get.

Ayya Khema (Who Is My Self: A guide to Buddhist Meditation'):

"Here a monk, on seeing a visible object with the eye, does not grasp at its major signs or secondary characteristics. Because greed and sorrow, evil unskilled states, would overwhelm him if he dwelt leaving this eye-faculty unguarded, so he practices guarding it, he protects the eye faculty, develops restraints of the eye-faculty. . . On hearing a sound with the ear, . . . on smelling an odor with the nose, . . . on on tasting a flavor with the tongue, on feeling an object with the body, . . . on thinking a thought with the mind . . . He experiences within himself the blameless bliss that comes from maintaining this Ariyan guarding of the faculties. In this way . . . a monk is a guardian of the sense-doors.

When the eye sees, it simply registers color and shape. All the rest takes place in the mind. For instance, we see a piece of chocolate. The eye sees only the brown shape. It is the mind that says: "Ah, chocolate! That tastes delicious - I want a piece!" Not to grasp at the major signs or secondary characteristics is to stop the mind from doing exactly that. We can practice this easily with anything we either very much like or very much dislike . . . . . . If we are easily swayed by what we see, the best thing to do is to recognize the sense-contact and stop the mind at the perception, the labeling. It is very hard to stop it before that. So, for example, if we see a person, or even think of a person, for whom we have hate or greed, someone we either dislike or long for intensely, we should practice stopping at the label, person friend, male, female. Nothing further. The rest is our desire. That is what is meant by guarding the sense-doors. Our senses are our survival system. It is much easier to survive if we can see and hear than if we are blind or deaf. Most people assume, however, that the senses are there in order to provide them with pleasure. We use them in that way and become angry when they fail to do so. We then blame the trigger. If someone displeases us, we blame that person. It has nothing to do with the other person, who, like us, is made up of the four elements, has the same senses, the same limbs, and is looking, as we are, for happiness. There is nothing in that person that is producing displeasure. It is all in our own mind.
Exactly the same applies when we think another person will provide us with pleasure . . . There is no reason to look to that person for pleasure or blame then for not providing it. All we have to do is see "person". Nothing more. There are so many "persons" in this world, why should we allow this particular one to arouse our syndrome of desire-distaste? If we guard our senses, we guard our passions, which enables us to live with far greater equanimity. We are no longer on that endless seesaw; up, when we are getting what we want, down, when we are not, which induces a continual inner feeling of wanting something that just escapes us. Nothing that is to be had in the world, anywhere, under any circumstances, is capable of bringing fulfillment. All that the world can provide are sense-contacts - seeing, hearing, tasting, touching, smelling, and thinking. All are short-lived and have to be renewed, over and over again. This takes time and energy, and here again it is not the sense-contact itself that satisfies us. It is what the mind makes of it. Guarding the sense-doors is one of the most important things we can do, if we want to lead a peaceful, harmonious life, untroubled by wanting what we do not have, or not wanting what we do have. These are the only two causes of dukkha; there are no others. If we watch our sense-contacts and do not go past the labeling, we have a very good chance of being at ease."

I respect the other answers given, however I would like to approach the answer from another angle.

I suggest not making a decision one way or the other. The Buddhist precepts ask you to refrain from irresponsible sexual actions; these can be understood as actions that bring harm to some one—including yourself. Not seeing prostitutes would be just one aspect of this. Not cheating on someone or being with someone else’s partner are other obvious examples. But a relationship is much more than sex. And here is where my answer differs from to many of those above. Being in a caring responsible relationship allows you to practice loving kindness and compassion in many ways that are not available to someone who is not. If children are involved—either your own or from a partner’s life before you—then the opportunities are expanded even more. There are few roles more important then being a good compassionate parent preparing a child for this world, and for them to be good people in this changing world. Another is being a reliable partner for someone as well. But this doesn’t mean giving up the Dharma or converting those around you to it.

Personally in my early twenties I decided to experience voluntary celibacy for a period and I chose 6 months. I found it a very useful period. But I did not do it again, I’m now married with a stepson. Life provides many opportunities to practice the Dharma and improve myself as a person. I would argue more opportunities than if I was a celibate lay person.

I suppose it comes down to how you approach the Dharma—is it towards personal awakening or more towards becoming a Bodhisattva? Be aware of extremes and their attraction—remember the Buddha chose the middle path.

As you've said, it all varies from individual to individual. The bottom line is one should not do what other people expects one to do. Instead, do whatever is best for oneself in terms of peace, happiness, and most important, suitable and favorable conditions to the learning, contemplation, and practice of the Buddha Dhamma. Please see DN 29, where the Buddha taught about the 10 kinds of disciples that make up His spiritual community. Out of those 10, 4 are from lay folks like us: celibate laymen, householder laymen, celibate laywomen, and householder laywomen. Give it a careful read and it could be a useful guide to help with your inquiry. Good luck..