1. It’s like dating a girl with a regular best friend, but she’s around a lot more often, if that’s possible. Not only is she at every social event with your girl, but she’s at all the family events too. Your alone time seems a bit more special since it’s a sought after commodity.
2. Inevitably you’re all at a meal together and one of them erupts into a fit of laughter and brings the other one with her. You worry one or both of them will asphyxiate, but you’ve seen it too many times before to really worry. You just sit back and wait for them to be able to breathe long enough to resume the conversation.
3. The amount of time your girl spends on the phone seems insane, especially for a millennial. There’s something about family that makes you prefer their voice to text messages, maybe it’s because you spent so much time with them on the phone before texting became popular. The calls are before work, and after work. They’re figuring out what to do about a difficult boss, and whether she could get a bench for her entry way, and — you’re sure — dissecting every detail of your relationship as soon as you leave the room. The sheer volume of conversations you’ve overheard between the two of them could fill an encyclopedia.
4. You’re constantly amazed at how quickly two people can go from fighting and making fun of each other back to BFFs.
5. Just from overhearing their gossip you’re an expert at their family tree and you know which aunt is crazy and which uncle is creepy and which cousin is prone to dramatic fights at every family gathering. It actually makes you fearful at Thanksgiving because you worry you might mess up and let on to Cousin Amy that you know her husband isn’t her baby daddy — something you definitely aren’t supposed to know.
6. Even though they don’t live together, they somehow still share a wardrobe. You’re aware of this because of the frequency with which you’ve heard, “remind me to bring my sister’s see-through tan sweater” with to brunch, and (probably), the frequency with which you’ve forgotten to do so.
7. They won’t admit it, but they’re both competitive with each other. It’s more cute than concerning, they’re best friends, but they’ll always be sisters first. The jokes about who is “the pretty one” are (mostly) just jokes.
8. You become best bros with the sister’s boyfriend or husband because if you didn’t, there’d be an awful lot of silent time between the two of you when the girls disappear into private conversation.
9. You will be constantly reminded by the older one that she is older, and therefore, necessarily, wiser. This will be rebutted by the younger one who will make an over the hill joke. Like clockwork.
10. The longer you date, the more you wonder whether you’ll ever be as close as they are.
11. They still haven’t grown out of the occasional roughhousing episode.
12. When you started dating your girl, you were made VERY aware by her sister that her approval is required for the relationship to continue. You treat the sister like a sort of platonic extension of your girlfriend, at least in the sense that you’ve paid for way too many of her meals.
13. If you’ve ever seen someone trash talking the sister in your girl’s presence, you’ve seen her go full on mama bear. As much as it’s okay for them to fight and make fun of each other, it’s not okay for anyone else to do the same. She will have her sister’s back, and this trash-talker won’t know what hit them.