H.F.
J.,
I'm sure that your son is really trying to deal with his emotions right now about his dad leaving. Some children have a harder time dealing with change. You don't say how much his dad is still involved with him but even if he was still seeing his dad daily, this would be a difficult change for him. It makes it more difficult when they are younger like him and can't always recognize or express what is upsetting them. Be patient and consistent with him. With anger issues that involve kids being violent to themselves or others, usually a time out works well but it sometimes takes several time outs before you can see that they are working. The key here is to be consistent. When he starts having a fit, pick him up and tell him that you understand he is upset but his behavior is not acceptable behavior. That even when he is upset, he can't hurt himself or others. Then sit him down for his time out. Most books say that a time out should last no longer than the age of the child. We have our own little change to this at our house. It is not really a time out while they are still having the fit. If it is just a temper tantrum, I put the child in time out until they are done with their fit. I check on them often but I usually put them on the sofa or in their room. Once they are done, I usually have them say they are sorry and give them a hug to reassure them that I still love them. If they won't say they are sorry, then they need to sit back down for the (my son is 2) 2 minutes. If they haven't said that they are sorry, I usually wait until after the time out and then again, I reassure them that I love them regardless of their behavior but they have to learn how to behave so they don't hurt themselves or others.
I know (personally, I'm pregnant with my third and due in August) that this can be even more difficult while dealing with all of the extra hormones and symptoms that pregnancy can throw at you. Sometimes, they fits can really make a person feel inadequate or frustrated as a parent. It is during these times that I take their timeout as a time out for me as well. I will put them in their time out and step into the other room for a few much needed deep breaths and a moment of calm. Then I feel better equipped to deal with the fits and it also gives me a chance to realize that my child is dealing with a lot of emotions that I as an adult sometimes have problems dealing with and they need the time and the space to deal with them just as I do. It makes it understandable why they may have fits but not acceptable. That is why time outs are effective in these cases because they give the child the time to sit down and deal with some of their emotions without other distractions.
Good luck with your little guy and the new one on the way. I hope that my little bit of personal insights with my own children helps you as well.