What sentence can I get for obstruction justice?

Okay, me and my b/f were fighting and having a bad night. Told him I could not take it anymore and that I was going to take him back to his mom. We live about 2 to 2 and half hours away from his mom. Well we were on the road, still fighting, I tried to p a semi- smaller size-like a dump truck- and he was coming into my lane a bit. So I slowed down so I could get behind him since I was afraid he could not see me and was either falling asleep or trying to get over. I was driving a small dodge neon. And I don't trust it so I would not speed too much... hence not speeding up to get around him instead of falling back. Anyway, he clipped my right fender and blew out my tire. I managed to get to the shoulder of the ramp. At this point my b/f was really screaming at me and we didn't have the cell phone. The driver never got out, so I started to walk to look for a phone. Luckily a lady was coming up behind me and offered to help. If she was not older I would not have gotten in the car... but felt it was okay. So we drove around for a bit but could not find a phone and the area was HORRIBLE. There was no way even if I did, would I have gotten out. So we went back and there was no sign of the car. Now, my b/f had stayed with the car. He had been drinking, but only had 2-3 beers at the time, so we wasn't drunk. The truck driver radioed it in ( i found this out later) to his company who called the police. I couldn't have been gone for more then 25 mins. I thought he had ditched me. Yes, he has done it beofre... so its not a stretch to believe other wise. The lady offered to take me somewhere, but I didnt know anything around there and neither did she, so I gave her some money to take me home. About an hour away. The next morning, I got a call from bf saying they arrested him and impounded the car. I went and picked him up and went to see what was going on with the car. I talked, wrote out my statement, and they said it was fine,. Today, I got a call from a Det. that said he was going to charge me with obrstuction of justice for lying since they knew my b/f was driving. I guess the truck driver didn't see me. They never did a soberity test or breath test on him... he wasn't drunk they said. I went to explain what happen right after I found out that the police did show and he didn't ditch me. There were no witnesses, the lady who picked me up didn't see the accident, and I never got her last name ( if I did I do not remember it). The cop said since I don't have any details ( time of wreck, the lady's name, or the fact that I did not comtact that night) he knows I am lying. Says he will charge me and come get me with the warrant to arrest me. So, I know I should have stayed, but I wasn't running, I was trying to get help. IF I knew I would have to prove my innonence, I would have gotten the lady's last name, addy,and plate number. I also left all my info in the car for my b/f in case the cops got there before I got back ( the insurance and other car papers). So, what do I do? I told the truth, but the cop says that since the truck driver never seen me ,then I couldn't have been there. I think thats unfair. I never seen him either, but I knew he was there. And my b/f story is the same as mine. So IF they do charge me, what can happen? Or what should I do? Also, the cops say he is coaching me along with the whole story, but i gave my statement over the phone before speaking with him. Any and all help would be great.