Upvote:4
I assume that you hold an Australian passport which you can use that to travel to Malta without any problem as long as it's not more than 90 days. Now the question is to go back to the UK. One thing that I know from my friend who used to be in the same position as you (he married to an English girl) is that if the immigration officer didn't think your marriage is a sham. They wouldn't ask where your husband is. Or they might ask how did you get the residence card. And as long as you can provide them with an honest answer they can at least ask questions (I'm not saying they cannot reject your entry). But it's unlikely that if you're husband is outside the country and you'll be rejected your entry. So, they might ask what're you doing in the UK and how long. You can just give them an honest answer.
And as you're Australian you can come to the UK with your Australian passport anyway. So, I don't see any problem for you to travel to Malta and back to the UK.
One thing to note that if you want to apply for a British passport you should not stay outside the UK longer than 180 days in 5 years.