I can't add to the analysis of the situation, but communication - or the lack of it - seems to be a key issue here. The dialog needs to be objective and calm. Sometimes that is a challenge when the issues themselves involve emotions.
One thing that can help is writing down your thoughts / feelings. This does a couple of things. First, it gets them out of your head and in front of you where you can see them. It gives you a chance to ask yourself, "why do I think this?" Or "why do I feel this?" Why is the most important question you can ask yourself, because often the answer isn't what you think it is when you're grasping in mid-argument. (Your husband should do the same.).
When you two have a conversation about it each needs to approach the other with respect. Respect that each person's point of view is valid, nobody's the bad guy, and no one needs to be put on the defensive. The conversation is about what each person needs and wants - two very separate things - and how adjustments can be made so that everyone has his / her needs met.
The very minute one of you says (or even thinks) the words, "you should...." you've put the other on the defensive, tried to make your needs and feelings the other's responsiblity, and are no longer owning your own shit. That is not the road to mutual understanding.
Now we would hope that you both have the desire to help each other meet your individual needs, right?
So for example, maybe one of your needs is the need to know what to expect. (Kind of sounds like it from what you've written.) So maybe, you and your husband work out a schedule, as some have already mentioned, or that you need x amount of time notice.
Now if your need is to have him be at your disposal 24/7, and he is allowed to be with his gf only upon your whim, then that's probably not going to fly. The gf is a real human being with needs and feelings all of her own; not just some toy. So each person, in considering his / her own needs must consider the that the others have needs that are just as valid as one's own. It helps to make a concerted effort to put yourself in the others' place just to get an objective shot at how the situation may look to them. It also helps to realize that everyone else is just trying to get needs met, no matter how ineffective and ungraceful, and no one is purposefully setting out to hurt the others in the group.