When he comes for his stuff try to look like you are fine. Don't talk about your relationship at all.
Yes, it works. It doesn't always work. It works better than crying, begging and pleading.
It isn't really important if there is another person involved, unless that is a deal breaker for you. It really doesn't change what you do, if it isn't a deal breaker.
You might look at the top thread in the Midlife Crisis forum. Look at the links in the first post. MLC is a possibility, perhaps even a probability. If you think it is MLC, you might want to post on that board. It might take a bit to get going, but you will get incredible support!