You mentioned that he wants to learn how to crochet. Could you teach him, or perhaps learn how to alongside him?
Everyone is very quick to leap to "put him in care!" and/or "have him sectioned!" - but I don't think they fully understand not only how difficult it is to do either, but also that you will lose your son completely. And as broken and exhausted as you are, OP, I don't think you want that. Not really.
At 14, your son is making choices. Does he understand that for every choice, there is a consequence, be it good or bad? Is he crying out for attention from you? Or is he flailing because he feels that he has to be "the man of the house"? You might get along with his stepmother, but does he? Does he feel like she's constantly studying him, looking for faults, and react accordingly? Does he resent the fact that you and his father are no longer together? Does he feel the weight of adult responsibilities bearing down upon his shoulders, and not know how/what to do? Was his father anything like this during your relationship with him?
He may well have a personality disorder, or other MH issues... sure. That's not improbable. Having him speak with a psychologist may well help (it did with my daughter)... but you can't force him to engage, unfortunately, so be prepared for him to close himself a little further away from you, if you seek psychological help for him.
My son, 16, went through a stage of very similar behaviours almost 2 years ago. It turned out that he thought that was how he was expected to behave, because he's the only male in the house, and his friends had been relating how their fathers/stepfathers behaved - so he daftly went with their examples. He didn't stop until, essentially, I had a complete breakdown through stress and he realised that he was the main cause. Two years on, he's a typical teenage boy - likes to sleep, hates homework, loves gaming... but there's no longer intimidation tactics and emotional warfare going on. One way back from the brink for us, was I asked him to show me how to play one of the games he liked. And that diverged into playing cards together. It's our "mother/son thing" now - and it's worked. Crochet may well be your son's saving grace and what brings him back to you. Either teach him, or learn together (there are plenty of tutorials online, but be aware of whether you're learning the American or UK way!) - and the precision of it, the accomplishment he'll feel when he has a finished item, the rhythm of it may well help quieten the rage of his mind. It's worth a try, surely?
I know it's hard, OP, but you're his mum. And he's crying out for attention - albeit in a horrendous way. Take some comfort from the fact that if he truly wanted to kill himself? He would have cut himself last night. But he got your full attention (and then the police's), didn't he?