The Nightcap
A lot of non-monogamous relationships eventually run into the overnight date situation. Some of us have prepared ourselves to deal with the dates when our nesting partner returns home. Knowing that your partner will return can minimize some of that overwhelming anxiety, jealousy, and envy. However..transitioning to overnight dates, you have to process a different facet of emotions and possible issues.
Expectations
Set realistic expectations and discuss them with your partner before their date. You both may give a strict return curfew of 7 am - be realistic and open to a later arrival to consider breakfast or traffic. If there are boundaries related to barrier use, express this again. This is not the time to assume everyone is on the same page. Take your time with this discussion.
The Polycule
If you have a network system of partners and non-monogamous friends, see if they could lend some support. Plan a game night or video chat to help process any anxiety or jitters.
Don't Wait Up
As tempting as it may seem - don't wait up. You already know your partner is not returning until very late or in the morning. What you can do instead is plan for their return. If you are comfortable, set out their morning routine necessities. Put the coffee pot on a timer for their arrival. If they are returning in time for breakfast, make breakfast.
The Evening Routine
If you have an evening routine, stick to it when your partner is on their date. Do not try and make their date ceremonial in nature. There is no need to mourn their absence symbolically. Doing this is crucial for not only your peace of mind but also for establishing a foundation for your autonomy and self-care. If your evening routine includes your partner, depending on what it is, see if they will do some of it with you before they leave. If you are not the routine type, look for something to watch, join a 24 hr chat forum like CH or R-ddit, read a book, or tackle one of your neglected hobbies. While it is okay to "lose" time, you do not want to be up till 3 am watching horror flicks if this is not something you would typically do. Incorporate some tea, candles, and relaxing music to wind down if necessary.
The Breakdown
For some people, no matter how long they have been non-monogamous, an overnight date could be heartbreaking. So what do you do when the feeling of loss is too great to bear? Sit in it. If you are in tears, hysterical, or overwhelmed with grief, anger, and jealousy, that heavily reflects a possibly codependent relationship. There is something to be said if you feel like you have to call your partner to tell them to come back home and there is no emergency. If you have a mental illness and have issues with attachment, this is the time to utilize your prescribed medication and coping mechanisms.
While your pain is valid, short of an emergency, try to minimize how much you contact your partner throughout the evening. Jot down or voice record your feelings to talk about the next day.
Keeping in Contact
Some people may find texting the happy medium. Texting, sending pictures, videos, and even chatting on the phone can be fine if everyone agrees. Unpopular opinion - this includes the person(s) your partner is on a date with. They may not mind the contact, but who wants their entire evening dedicated to face timing you to sleep?