This is something which - these days - is very much up to the individual's circumstances, and person beliefs.
If your careers advisor is in a stable relationship, just not married, that what lots of people do these days, many people live together for years (if not all their lives) without getting married.
The worry at the moment, and the message which the school is trying to get across to young people, is that babies shouldn't ideally be conceived to teenage parents by accident, or just because you feel like it, or because life would be better if you had a baby - having a long term relationship, married or not, is a much better basis for bringing up a child.