I don’t think a man and a woman living together is a sin in and of itself. However, playing “Married” by sleeping together and acting like everything is fine and you are practically married makes a mockery of the sacrament of Marriage.
Assuming you and your boyfriend are living like brother and sister and not having relations, it still can cause the sin of “scandal” by living together while not married. You are pregnant and people are going to assume you two are still sleeping together. THAT, if it cause another to sin is “scandal” and it helps others sin by you and your boyfriend co-habituating because you are helping to perpetuate the secular thinking that it is perfectly acceptable for a man and woman to live together, have sex before marriage and even have a litter of children out of wedlock. And, as we know, these things are not acceptable behavior from someone who is supposed to be Catholic. What about when a friend says “I have a friend who is Catholic and she lives with her boyfriend” that makes The Church look bad to non-Catholics. It is not being a representative of Christ that we are kind of supposed to do by imitating him and letting our light shine. Causing “scandal” is a grave matter and if done with all three conditions met (fully knowledge, grave matter and 100% consent) it is a mortal sin.
I would definitely talk to a priest. I know life is not easy, so you may not be able to just move out like I am sure some people will tell you that you must do. But if you can, I would. If you cannot, you must live like brother and sister with your boyfriend. But you definitely need to talk to a priest. Like if you cannot find him today, at least call your parish and leave a message. Talk to a Deacon if you can find him. Good luck and God bless.
