What can we do if we're only horny when we can't have sex?

My girlfriend and I (both females) have the same problem: we are super horny when we know we can't have sex, like if there's no time and we have to leave, or when there's someone around, or we simply planned something else. But when we actually can have sex, we're not aroused, especially me. It's like I wanna have sex but I physically don't feel like it unless I know we can't do it.
I know it probably has to do with the adrenaline rush of doing something we're not supposed to. I also feel like my arousal is "fake" whenever we can have sex, because I kind of planned it in my head already, so it feels less genuine than when we're not supposed to do it. I also have difficulties with intimacy, so I feel like being unable to have sex makes me feel kind of safer, as if I'd be telling myself "I know nothing will happen anyway, so let's just be myself and feel whatever I want."
This situation leaves me really frustrated, because whenever we do have sex I'm not really aroused tbh. And the only times I feel really horny, we just can't act upon it.
Do you have tips for this situation? I was thinking of ways to "fake" this feeling of not being able to have sex, even when we can? We both can't think of ways to get around it...