Wow! You've got a couple of big issues here. I think the first question would be - is he taking any medication? It sounds like hes highly impulsive and there are medications that can help with that.
Concerning the girlfriend - have you spoken with the girls parents? I know that would be an incredibly awkward conversation but maybe you all can work together to address it?
This book called "Adolescents on the Autism Spectrum" has good reviews on Amazon, maybe check it out?
http://www.amazon.com/Adolescents-Autism-Spectr...(Phone number can only be seen by the question and answer creators)&sr=1-3&keywords=autism+teenager