how to eradicate past smaskaras

Ven.Yuttadhammo bhikkhu has given you proper advice. Being true to monkhood is being rooted and grounded in a Life of celibacy. The benefits of celibacy (sexual abstinence) are obviously not widely understood nor fully appreciated. Even though sex may be a natural, essential part of life, so is being stuck in a physical body along with all its severe restrictions, miseries and complications lifetime after lifetime. Celibacy is a change in the direction of sex and sensuality, not its repression. But this advice is easier said than done.

In becoming a Bhikku with an idea of performing the practice of breathing towards samatha and vipassana (calm and insight) without first attempting kayagata-satipatthana (mindfulness as regards the body), resembles an owner who yokes the still untamed bullock (an adult bovine animal) to the cart or plough without the nose-rope. Such an owner would find oneself unable to drive the bullock at his desire. Because the bullock is wild, and because it has no nose-rope, it will either try to run off the road, or try to break loose by breaking the yoke.

The Buddha, in one of the Suttas pointed out that the realm of sensual pleasures resembles the forest where the wild elephant enjoys himself/herself. The Buddha Sasana, "the teaching of the Buddha",resembles the open field into which the wild elephant is first brought out. The mind resembles the wild elephant. Confidence (saddha) and desire (chanda) in the sasana-dhamma resemble the tame elephant to which the wild elephant is hitched and brought out into the open. Sila-visuddhi (purification of virtue) resembles the stockade. The body, or parts of the body, such as out-breath and in-breath resemble the post in the stockade to which the elephant is tied. Kayagati-sati resembles the rope by which the wild elephant is tied to the post. The preparatory work towards samatha and vipassana resembles the preparatory training of the elephant. The work of samatha and vipassana resembles the parade ground or battlefield of the king.

Firstly what you have to learn to do is the Meditation on loathsomeness (Asuba). There’s a series of meditations called guardian meditations, which are very helpful in using skillful perceptions to get the mind in the right mood, in the right attitude, with the right understanding, as you come into the present moment. You’ll often find, as you’re sitting here meditating on the breath, that the problem is not with the breath. It’s with the mental baggage you’re carrying with you. So you want to open up the bags and throw out all the unnecessary weight. In practicing this, you see that we all have the same garbage inside ourselves. This contemplation is helpful because it’s a guardian. There are so many people out there you could feel lust for, so cultivating this protects you from inappropriate lust. Even if you’re not practicing celibacy, you need a way to guard yourself against that kind of vagrant lust. So instead of weaving all sorts of narratives you’ve developed around beauty, it’s good to teach yourself other narratives, other associations. While at it, you should learn to do what is skillful.

“And what is skillful? Abstaining from taking life is skillful, abstaining from taking what is not given... from sexual misconduct... from lying... from abusive speech... from divisive tale-bearing... abstaining from idle chatter is skillful. Lack of covetousness... lack of ill will... right views are skillful. These things are called skillful.”—MN 9

Also the Buddha said… “Come guard your sense-faculties; be the master of your senses. When you see something with the eye, do not get attracted to it by its appearance, but treat it with self control. So allways be mindful by controlling and guarding your senses the eye, the ear, the nose, the tongue, the body and the mind.