Can my boyfriend of 3 months kick me out and not let me get my belongings?

Since there is no agreement for you to be a renter, you are a guess who he can order to leave at any time, but he can not keep any of your property. He has to allow you the reasonable opportunity to get your possessions. Tell him if he does not, you can sue him in Small Claims Court for their value or ask the police to help you recover the property. Point out to him that if the police come, they may look around and find the new girlfriend's drugs and arrest both of them. The cops will likely know she is a drug abuser by looking at her. The guy is a predator taking advantage of women who are helpless; he probably picks a woman up and every few months selects another woman when he tires of the first. You should also check to see that he has not given you some sexual disease, since he is likely to catch one sleeping with a prostitute and some many women using unclean needles. You are lucky to get rid of him.