My rule of thumb is that when either of my two children get physically agressive for whatever reason, it's the naughty corner for them. It doesn't matter what the how's, why's and wherefor's of their behavior is, if they push, hit, bite and the like, they get the corner because those behaviors are never acceptable. They stay in the naughty corner for a minute for each year of their life (3 years = 3 minutes) and, afterward, I explain to them why they were sent to the corner and make them apologize. You need to be consistent about this because, if you are not, then you are sending your child the message that if he behaves a certain way, mommy may or may not punish him so why not misbehave and take your chances.
I understand that it may be difficult for you and your son while your fiance is away and that maybe this is affecting your son's behavior (still not a good enough excuse for assaulting someone else or letting this behavior slip), so maybe at this time, you will need to plan some extra special activities to take his mind off the fact that his daddy is not at home. Take him to Chuck E. Cheese one day, play in the sprinklers the next, invite friends over for a playdate another day. The two of you need down time as well but try to see what you can do to structure his day a little bit more and get him more social interaction to distract him while daddy is gone.
But, all that said, kids who are 3 do bite, kick, push and scream. It's a natural course in their development. It's up to us parents to teach them that this behavior is always wrong and to teach them more constructive replacement behaviors (talking instead of hitting, squeezing a teddy bear when you are mad instead of knocking over another kid) so that they can control themselves as they get older.
Good luck to you and your son.