A brahmana generally remains a brahmacari throughout his entire life, but although some brahmanas become grhasthas and indulge in sex life, they do so under the complete control of the spiritual master
SB Canto 7
All the rules and regulations apply equally to the householder and the sannyāsī, the member of the renounced order of life. The gṛhastha, however, is given permission by the spiritual master to indulge in sex during the period favorable for procreation.
It is sometimes misunderstood that a gṛhastha, a householder, is permitted to indulge in sex at any time. This is a wrong conception of gṛhastha life. In spiritual life, whether one is a gṛhastha, vānaprastha, sannyāsī or brahmacārī, everyone is under the control of the spiritual master. For brahmacārīs and sannyāsīs there are strong restrictions on sexual indulgence. Similarly, there are strong restrictions for gṛhasthas. Gṛhasthas should indulge in sex life only in accordance with the order of the guru. Therefore it is mentioned here that one must follow the orders of the spiritual master (guru-vṛttir vikalpena). When the spiritual master orders, the gṛhastha may accept sex life. This is confirmed in Bhagavad-gītā (7.11). Dharmāviruddho bhūteṣu kāmo 'smi: indulgence in sex life without disobedience to the religious rules and regulations constitutes a religious principle. The gṛhastha is allowed to indulge in sex life during the period favorable for procreation and in accordance with the spiritual master's order. If the spiritual master's orders allow a gṛhastha to engage in sex life at a particular time, then the gṛhastha may do so; otherwise, if the spiritual master orders against it, the gṛhastha should abstain. The gṛhastha must obtain permission from the spiritual master to observe the ritualistic ceremony of garbhādhāna-saṁskāra. Then he may approach his wife to beget children, otherwise not. A brāhmaṇa generally remains a brahmacārī throughout his entire life, but although some brāhmaṇas become gṛhasthas and indulge in sex life, they do so under the complete control of the spiritual master. The kṣatriya is allowed to marry more than one wife, but this also must be in accordance with the instructions of the spiritual master. It is not that because one is a gṛhastha he may marry as many times as he likes and indulge in sex life as he likes. This is not spiritual life. In spiritual life, one must conduct one's whole life under the guidance of the guru. Only one who executes his spiritual life under the direction of the spiritual master can achieve the mercy of Kṛṣṇa. Yasya prasādād bhagavat-prasādaḥ **. If one desires to advance in spiritual life but he acts whimsically, not following the orders of the spiritual master, he has no shelter. Yasyāprasādān na gatiḥ kuto 'pi. Without the spiritual master's order, even the gṛhastha should not indulge in sex life.