Thank you for writing to Just Answer!
It sounds as though your trust has really been broken this time. Staying overnight with a woman while your partner is away is a good indication that he is most likely cheating.
It doesn't sound like the two of you are communicating very well at the moment...he doesn't understand why you're going out without him, and you have reason to believe that he's been cheating.
One of the favorite defenses of people who are cheating is to accuse the other person of having issues because they don't trust them. This is an attempt to deflect the attention away from their cheating.
It sounds like things have deteriorated to the point where there really isn't a relationship anymore. Usually couples are happy to see each other after a week apart, but it doesn't sound like this is the case with the two of you.
It may be time to re-define how the two of you relate to one another. If neither of you can afford to move out, it will make things much more difficult.
Perhaps the conversation could center around "how can we continue to live together, but not be a couple?"
If this isn't what you want--if you still want to try to make this relationship work--then you need to be more upfront and honest about why you're spending time alone, why you're keeping your distance. If you want to be with him, keeping your distance won't help. And he's left playing a guessing game. Men are very bad at figuring out what women are thinking.
There's a good book that I can recommend to you that does a wonderful job of explaining how men think, and what motivates them. It also explains what motivates women, so it would be good for him to read as well, if the two of you still want to be together. How to Improve Your Marriage Without Talking About It
Whenever you wonder about how to have a conversation with a man, some guidelines to keep in mind are:
-Talk when you are calm, and know what you want, and what you want to say
-Don't start the conversation with the words "we need to talk"--that sends men into a defensive posture before the conversation even starts.
-Most men are more receptive to talking about the relationship when they feel physically connected. Don't start the conversation while he's distracted.
-Some men do better with talking when they can move around..or not have to sit face to face with you. Try taking a walk together and saying what you need to say.
Try to figure out what you really want: the relationship or your freedom. If you're ambivalent, it will show in your actions and your conversation, and will just lead to more hurt and confusion. And if you really don't know what you want anymore, then that could be the basis of your conversation--an honest admission that you don't know what the two of you mean to each other at this point. Something like "I'm feeling really confused about how we're interacting with one another, and wonder if you're confused too..."
At this point, it seems you have nothing to lose by being honest with him, and possibly much to gain.
I wish you the best as you try to get communication back on track with him,