I don't know that that follows. Just because the Templars aren't following any promises with regards to sexual behavior doesn't mean they didn't make any.
The Chantry does not forbid sexual encounters, in fact it's the exact opposite. Those who wish to aspire to a higher form of faith, or rank within the church may or must take certain vows. An initiate is the lowest rank in which such vows are necessary. The Affirmed as you likely know is just under Initiate most likely, as they choose to affirm their belief in the maker, but take no vows to abstain away from sex or other inhibitions.
It's just as like Templars aren't require to take a vow of chastity, as sex was is just as much a form of recreation as it is procreation in such times, and people needing away to blow off steam is always going to be needed, a ****** house is such a place and the Chantry likely overlooks such discretions because it's necessary in order to keep the troops focused. Still it is possible some chantry brothers who have taken their vows, may have taken their own personal vow not acknowledged by the church in order to better honor their faith, and simply choose not to have sex, or succumb to the temptations of desire. Cullen was a full fledged Templar in DAO but he still had feelings for a young mage even though it was ill advised as such things likely are for obvious reasons.
The only thing is that I can see is that Templar's are always on duty, they have little in the way for personal affairs such as raising a family or being a homely mother or father since they vowed to serve the maker by taking up their holy task.