Is my boyfriend trying to kill me and my children?

I have been seeing this guy since July 2012. at first impression he seemed like a charming, well-intentioned, nice guy. As our relationship progressed he would start making comments after we had sex, or on the phone to the effect of "you ever leave me, you're dead" or "if you ever broke up with me I would shoot you and then shoot myself". and then he would add a familiar "JUST KIDDING!" afterwards and I'd be left wondering if I should fear for my life or that of my childrens. He has tried to ciphon gas out of my car to keep me from leaving his house, this past summer I overdosed on OTC sleeping aid pills and he KNEW what I had tried to do, and watched me fade in and out of conciousness, struggle to breathe and had difficulty even making out words all night until I finally fell asleep. I should have been brought to the ER, instead he knew I could have died and watched me struggle for my life that whole night. At that point I should have left him, and acknowledged the truth that I was with someone that DID not care about my life, Instead I went to treatment and a halfway house and got out a month ago and since then, I have had two different incidents that leave me wondering if he is subtly trying to kill me or cause long term harm to me and my children and family.

The first incident happened at his best friends apartment, I came over to see him there and his roomate Josh was home, we started drinking and my boyfriend went into the back room and just stayed there laying in the dark for 20 minutes, me and his friend decided to leave and we were gone for at least 4 hours seeing other friends. We get back to his apartment and realize the door frame to his front door is stripped on the dead bolt side, like the entire siding of frame is stripped away, our thoughts afterwards was so that my boyfriend was able to gain access at anytime, we got into his apartment and out of the corner of my eye I saw movement outside from the window, none of the lights worked in the place, the flourescent kitchen hanging light was broken and flickering and all the major appliances in the entire apartment, including the dryer and washer, were all unplugged. I began to get a bad gut feeling that something wasnt right. I had his roommate check the stove and sure enough some of the stuff behind the stove was messed with and was moved away from the wall. We realized the propane tank off the gas grill outside his house was suddenly missing. Willie came in thru the front door and attacked Josh. Josh was already by this time having breathing problems and said he felt like everything was in slow motion. After the fight, my boyfriend "left" and his roommate was laying on the living room floor struggling to breathe, having an anxiety attack, he threw up afterwards and his muscles began to twitch and he lost basically all muscle coordination. I started having the feeling of panic, my heart started racing rapidly and I felt like I couldnt breathe. I stood up and opened the door and breathed fresh air and began to feel better. I mentioned to his roommate that something was really wrong. I googled natural gas poisoning and came to two conclusions that my boyfriend was trying to do. Either build up enough natural gas in his roommates apartment so that when we walked in and tried to flick on the light switch, the electric current would be enough so that there would be an explosion. Or leak natural gas/carbon monoxide into the apartment and watch us die while he was hiding out in the garage. I tried to fathom this whole situation by myself afterwards, my boyfriend adamently denies all of this, but has begun to unravel. I have caught him in several lies, and when he gets caught he admits fault but still tries to outwit me and think he can get by my sixth sense and gut instinct. I have a high sense of danger or when things arent right and I just feel like he would intentionally inflict damage to something in my home or in my car that would cause severe long term damage such as carbon monoxide or natural gas exposure. In my vehicle, my check engine light has come on since this incident, and when riding in my vehicle with my children or on my own, i get terrible headaches, feel like i cant breathe and smell an exhaust fume. Tonight I had to drive with my child to the clinic for a medical problem and it seems we both are short of breath tonight, and have slight impetigo. The other incident involves him making himself appear as mr. nice guy, has all the right words, says all the right things, lies like its nothing and has abusive tendencies from his past including reckless endangerment of his ex girlfriends current boyfriend and trying to run him off the road. I am scared to leave him for fear that if I do, he will harm the ones that mean the most to me, my mother and my children. Give me your advice, input, suggestions, and what any of this sounds like or means to you, if anything.