Borderline syndrome, esp. in males, and bipolar can be very hard to differentate, and, if he has started doing this later in life, I agree with Acension that PTDS needs to be considered. What concerns me is that you have a relationship with an unstable man with combat experience who will not admt he has a problem. Those i know, relatives and firends, who have been in the marines or in other branches of service and have come home with similar work history, deliberately avoid situations where violence might break out; bars on weekends, rowdy groups of people, teenagers on a wild night out, just because they know how easy it is for training to take over and that they might hurt someone. Right now, he has been sending you this stuff from a distance. what might happen if he has one of his episodes face to face with you? Will you be able to handle that? tThat time he was telling you to hurt your self and send pictures was very worrisome to me.
You are actually a person of great worthm, with or without him. You can't save him unless he's willing to work with you, it doens't sound as if he is. From someone who has had to learn the lesson tha hard way, please, value yourself enough to get out. It's harsh, but the harshness is born from a stranger's real concern. HUGGSSS, and let us know how it goes.