The term “cohabitation” strongly implies sexual activity, as it means living as a husband and wife.
The situation you find yourself in falls outside of the church’s prohibition on cohabitation, as you are living chastely as roommates. It is not ideal, but in the extreme situation that you have found yourself, it is not sinful.
Your focus should be on improving your financial situation, and discerning marriage with your boyfriend. The risk of scandal is minimal; you can explain privately to anyone you trust that is concerned, and simply not discuss the situation to those who have no particular need to know.
Please, be at peace, and work towards building a more stable, holy life.