My goodness.. I loved this. You should consider extending it:D my favourite romantic trio!

THIS IS SO CUTE OMG

I absolutely love what you've done here. Sirius, Lily, and James is the most amazing ship that I can't believe I hadn't considered it before! My favorite parts were when the pair admitted that they'd both kissed Sirius while drunk, and when James suggested the doghouse. Lol

I'll start at the end because I loooooved James having his key the whole time XD
Now I'll go back to the summary! I fell in love with this since I read the summary. It's strange, but I do think they fit well together and the summary showed that by itself.
Then there is the conversation Lily and James have. The spontaneous proposal really says something about them; I think it's the definitive proof of their trust in each other and in the love they have. I really think this is a wonderful story!

Okay, so this is adorable and fluffy and perfect. I love that Sirius is in love with James, because I'm a firm believer that it's at least partially true in canon, and I love how understanding you made Lily about the whole thing.
Sirius is sweet and lovely and adorable here, and I felt really sorry for him when he seemed to think it was a prank and then he smiles and just awww.
I loved it :P

This was definitely different from what I usually read but I did enjoy it. I really liked the little bit of extra history with the spin the bottle tale and when Sirius moved in with James. James having a key was also hilarious and so was their bickering, and you did a good job of not adding in 'unnecessary' dialogue and just showing us. I really enjoyed this, and James and Lily's open relationship was lovely - and so was the dorky way James proposed XD

I like how Lily was the first to notice that the attraction between the three of them were all mutual, and of course, think of a plan that would work for their situation. And since James and Sirius had always been close, it certainly made it easier for Lily to think of them all as one single entity.

Oh I love the part where James just blurts out a proposal and gets all adorably flustered about it, rambling on and on until he cuts himself off. And the thing that really struck him at the end was that they needed a better bed haha

I also like the little detail of how they didn't need to make many changes to add Sirius into their lives. It's like he was already so integrated with them that he couldn't possibly come any closer.

And you ended it perfectly again, like you always do. I love how it reconnected back to Sirius's earlier ironic statement about how James forgets his key.

This made me smile soooo much, I literally felt my spirits lifting to the skies. Of course this is more difficult than that, but it's also rather easy once some stuff has settled, and then you lie there with those wonderful people that share your life and wonder at the feeling of how this is just the right and normal thing for you. Speaking of experience, obviously, but the way you put this story into words is just what struck a chord with me. Thanks for this piece!
PS: I have an account here under the same name, just forgot my pw, that's why I posted anonymously

Oh my God, I literally love a trio story so much, and I think I may have found a way to tolerate James/Lily! I really like the idea of them inviting Sirius into their homes, and the strength of their relationship is so cemented that they can maturely discuss James's attraction to another man without Lily having a negative reaction.

This was written really well. I find it is usually hard to properly get across a threesome story without it flopping, but you have a really good handle on the situation. I spotted no SPaG errors. Well done, I really enjoyed this!

I still love this! I must've read it about twenty times by now!