There are a lot of changes that need to happen. To start with you'll need to be more strict on your punishments. Some kids do not respond to timeouts, so find something that he doesn't like. I never tolerated biting--NEVER. If one of my kids bit the other, I made them bite a hot pepper. It only took two times for my older son to not bite again, my younger son maybe three times. Still, I was consistent and that took care of that problem very quickly. I know that some will disagree with what I did, but biting is a very serious issue and cannot always be solved with timeouts or something of that measure.
As for his filthy mouth the answer is two-fold. You need to do something about yours (and your boyfriend's). If you don't want him to say those words, then you shouldn't be saying them. Kids will not accept that you can say it, but they cannot, they'll keep saying it if they hear it. So you'll need to curb what you say, and when you say it. At the same time, you'll need to explain that it's not okay for him to say it. Give him an alternative to say if it's such a big problem, tell him to say, "horse feathers" or something silly when things aren't going well. Maybe sit him down and come up with a word or words to say, and you use those words too. When you drop something say, "oh horse feathers" instead of what you normally say.
Whoever told you he needs discipline is correct, he does, but not just now and then when you're so upset about what he's doing that you can no longer take it, he needs it all the time. You need to constantly follow through. Don't just tell him he's going to go to time out, make him go. Don't just threaten him with a spanking, give it. Whatever you do as punishment you need to do, and not just threaten or suggest it, just do it, he'll get the point.
One last thing, I think maybe he does some of this stuff just to get your attention. Try spending some one-on-one time with him (same with your boyfriend) and encourage him to do things, not to not do things (meaning, instead of do not hit the dog, say, why don't we nicely pet the dog). Positive sentence or suggestions go a lot farther than tell some children what they cannot do.