What are some other (read details) shortcuts that might help you figure out if the one you're with is 'the one'?

When you’re done having sex and still want them to stick around?

Really wanting your closest friends to meet him/her and knowing that they will like this person, rather than worrying if they will or won’t; or knowing that it doesn’t really matter to you if they do.

I think you don’t know until twenty years have gone by. If you still look forward to waking up next to them by that time, they’re the one. Then again, even if they are “the one,” that doesn’t mean there isn’t another “one” you will soon meet. There could be more than one “one.”

Sounds like you found a short cut way to knowing for sure who is not the one. “The one” implies to me knowing this is the person you can be with for ever and ever, and I don’t really believe in a short cut way of knowing something like that. Or, I guess not able to know in a very short amount of time the person will be someone to spend the rest of your life with. When i was first dating my husband I was head over heals, would have married him after a few months, but I realize in retrospect that would have been very hasty, even considering 20 years later For me he is the one. There was really no way to know it after a few months of dating.

If you go out to a restaurant and see how that person treats the wait staff.

If you go to that person’s family home and see how they treat their parents/siblings/grandparents etc.

If you encounter a lost or injured pet, you check that person’s reaction (do they want to help or do they not care)

You encounter a friend or relative who is down on his luck and you check that person’s reaction (and reasoning) as to whether they will help or not.

You want to invite a group of your family members or your friends over to spend some time with your SO, you check his reaction. Is he happy to meet them, ambivalent, angry?

You get sick (not from being drunk, but ill) and need someone to help you go to the bathroom and help you to eat and possibly to help rub your back or your feet if you are in a lot of pain, you check their reaction. Do they jump in automatically without question to help you, do they act all squeamish and grossed out and not help you, or do they not help you because it doesn’t occur to them, or do they help you, but complain about it, or do they help you, but only in the minimalist of ways without actually making you feel better?

Do they let you know where they are going to be without making you feel guilty for needing/wanting to know where they are going to be?

Do they pay attention to the small things that you have said or pointed out and then act on them in sweet ways? Or do they not even pay attention to things that you have said or pointed out that were clear and obvious?

Ditto @Kardamom, absolutely!

There are no shortcuts when it comes to deep emotions and deep human relationships. I also don’t believe in the concept of ‘the one’. Instead I believe in the concept of a ‘good partner’ for life.