In Jain Dharma, the answer is:

• Yes – for Jain monks and nuns, sex is completely forbidden.

From the moment they take diksha (initiation), they accept the Mahāvrat of Brahmacharya (great vow of absolute celibacy).

What this means in practice

For monks/nuns (sadhu–sadhvi, muni–aryika, etc.):

• No sexual act of any kind.
• No deliberate sexual thoughts, fantasies, or looking at anyone with sensual intention.
• No physical touch done with sensual motive.
• They avoid situations, talks, places, and materials that can excite passions (kashāya), especially sexual passion.

The reason: Sexual desire is considered a strong attachment (rāga). It disturbs inner peace, increases karmic bondage, and blocks the path to liberation (moksha). A monk’s entire life is meant for self‑purification and ending karma, so complete celibacy is essential.

For lay Jains (shravak–shravika) the rule is different:

• They take a limited vow of brahmacharya – sex only with one’s own spouse, with restraint and responsibility.
• So the strict “never at all” applies only to monks and nuns, not to householders.

You can read a simple explanation about vows (including brahmacharya) here