I don't like the sound of physical threats. Having said that, your husband clearly does not consent to you having a boyfriend at all, so I think you will have to choose one and only one: husband or boyfriend. If husband you choose, I would suggest that both of you probably need to do some digging and find out what has gone wrong in your marriage. I would get a marriage counselor if possible.
Of course there is also the question of, is it worth trying to fix a marriage that's gone so far downhill that physical threats are being made? What are the extent and nature of these threats? Is it bluffing, or are you pretty sure your husband is serious about it?
If you're going to choose your boyfriend, then you should probably tell your husband you want a divorce. Why have him plug on with a situation in which you're in love with someone else but not him?
What do you you really want to do? is the big question.
Love means never having to say, "Put down that meat cleaver!"