It sounds like he likes to be a dominant person when it comes to sex. The first few times was him getting used to you; now that particular phase is over, he feels like he has more free reign to participate in the rougher sex in which to exert dominance and territoriality.
I can see two sides to this, one I see as hypothetical and the other I side with. The first being that you do like the rough sex. In that respect, you should speak more openly about it with him to distinguish certain boundaries of what is and isn't kosher during sex. With any sexual relationship, deep conversation is key while avoiding the superficial responses.
Secondly, and one I side with, is that he has gotten comfortable with having sex with you and is now exerting his more innate dominant side. Based on his comment of wanting the world to know "you're mine", I find that to be rather disconcerting. I would have a conversation about it in a public place and insist it be made there if only for your own safety. If he continues to refuse or gets overly hostile, then that's a humongous red flag to plug up your ass and take it somewhere else. Even if he is into dominant-submissive sex, there are boundaries that both parties recognize and respect; he clearly does not respect your boundaries.
My overall advice here is to not approach the topic with rose-tinted glasses. When asking the questions, listen to what he is both saying and not saying. Oftentimes, people sidestep questions or artfully leave out particulars that you were hoping be answered. If you feel too attached or are in the "but I love him" phase, please take a mental step back and view the picture as a whole.
As a sidenote, I had my share of one-night stands when I was in college. I was fucked by this one guy a few times; he was okay and normal with his style. After a few times, he got too comfortable with me and started getting kinda dominant with me; refusing to let me cop a feel of his dick to make sure there's a condom and stuffing his fingers in my mouth or even covering it. The last time we did it, I talked to him about it beforehand and he said I signed up for it before stuffing his barely lubed dick into my ass and practically raping me. Gave him the surprise of his life, though; lifted his 200+ body off the ground with my 115 pound self to the point he was forced to get off lest he fall and alert his neighbors. He immediately had me leave.
Point of that side note, don't settle for having your sexual boundaries continually being broken. Make your thoughts known and get away if things don't change. And don't be afraid to defend yourself if it's needed.