I never really had to deal with prolongued tantrums, but every child has some. some kids are just easier to deal with than others. (Once I had to physically drag a 5 yr old out of a friend's home when it was time to go home, force her into the car and was thankful for the child locks in the backseat, so we could drive around the corner and then stop and finally get her seatbelt on her. She simply didn't want to leave the fun of visiting and she was letting me know in the most embarrassing way she knew! but she did calm down when we got around the corner and were out of the situation. However, I have always wondered what those parents, whom I highly respected, thought about me as a parent ! tTey never mentioned it and it never happened again.)
It sounds like you and your ex lived together for almost 2 years of your little guy's life, and in the last 8 months, his life has radically changed, because Mom and Dad aren't together anymore. That's okay. It's better to be honest and live apart than to live together if the relationship isn't working. But ifyou are co-parenting, I assume your son is changing homes regularly, and at 2.5, he's learning about different homes, different rules, and he's head butting into them on occasion. He may be running a little higher emotional level than he would normally, because he's trying to sort it all out, including his own feelings of loss that he can't verbalize. And unfortunately, the parent at hand tends to get the anger, whether it's rightly deserved or not. It just is.
So you need to chart a course that says, "I love you. Daddy loves you. It's okay to be angry when you don't get what you want, but it's not okay to hit and hurt people." If he has his own room, and you are comfortable with allowing him to have a tantrum in his room, let him run off and go to his room when he is too angry to be polite. On the other hand, since he's young. If he doesn't obey when you tell him to, explain that he HAS to do it. You're going to count to 3, and if he will have to do it on the count of 3. Say 1, repeat the command, say 2, repeat the command. When you say 3, tell him the command again, and control him bodily, making him do it. This will give him some time to get used to the idea, and think about the fact that he has to do it. On 3, you may get some tantrums, esp when you start it, but for now you are stronger, and can force the obedience. (picking up a toy, etc.)
Everyone will think I'm a horrible mom, but I do not think your anger is a bad thing. While it feels TONS better to always be in control, it isn't horrible for a child to realize that if he or she acts like a wild animal, it is going to cause an effect that they don't like. I do not think a quick hand spank on the butt is out of line. I don't think it's horribly out of line to bite him back if he doesn't stop. He does need to learn that biting HURTS. My daughter was younger than that when she went thru a biting thing -- she thought it was funny. She'd nurse, and then bite. And I'd jump, and she'd laugh. hmmmm . . . then when you'd hug her, she'd cuddle up to your shoulder and bite you right on the bones. It HURT. I quit nursing, and she didn't ask for it anymore, so I figured it was definately time. But that didn't stop the rest of the family from shoulder love attacks. And at one point I remember finally giving up and biting her shoulder back. Not hard, but biting back nonetheless. (No marks) She stopped biting right away. She's a really awesome young girl, and has always been a very gentle person, even at her now ripe age of 15 -- and it was kind of a wierd thing to deal with given the rest of her personality.
If you can give your son WORDS, even if you are trying to do some mind reading and put some of them in his mouth, but if you ask him about his feelings, and ask him if he's angry about having to put the toy down, or something like that, whatever the issue is -- try to get the feelings out somehow, becuase when we don't have words for a situation, we do have fists. Another thing that might help is to get a book on baby sign language and begin to use signals while you talk. He might be able to use his hands to express things he can't verbalize yet, and it'll help him to express it physically without kicking, hitting, biting, etc. (I have a friend who babysat a special needs boy of about 3 -- and I'm not saying yours is a special needs child. She used a sign language book to help him to exrpress his desires (like wanting a cookie, or a drink or stuff), and it made a world of difference in his behavior. and if it worked with a special needs child, it might also work, and maybe even faster, for your son.
It's really an emotional thing. He can't express what he wans to say right now, so he's using his body to do it -- just as he did as a baby -- he cried when he wanted something, and you delivered it (usually food). It's now time to learn that we don't always get what we want, and it isn't quite so much fun to live that way. :-) the only other thing to do is to think through your list of what is critical, what is important and what rules are a waste of your time. You can't discipline everything, you discipline what behaviors are the most important to you. So we discipline out the things that send us into orbits of anger, and we discipline IN the things we most desire in our kids. There's a wide range in the middle that we have to relax and sometimes let go. Otherwise we would be saying no all the time, and our kids would grow up totally restricted and totatlly frustrated. So listen to yourself some, and see what's important and what things are unimportant. Disclipine the biggies. Praise the stuff you want to see. Hold the line tightly on the critical stuff (safety issues), and be sure the lines you draw in the sand are realistic for him to achieve. Most of all, plan fun things to do that he will enjoy, and that you also enjoy, so you can spend some happy relational time to offset those moments when discipline hurts both of you.
You also might want to discuss it with your ex to try to have similar household rules while he's young and while he's getting accustomed to the changes. It would make the transition time between homes a little easier on him.