Room to run
Neither one needs to be told to lighten up, and neither sees independence as a threat. Aries can go off to train for something and Sagittarius can go off to study something, and both come home with stories. Plans get made in a car and changed at a service station. People in this pairing often describe it as being with their favorite person to get lost with.
Laughter does a lot of work here. They can poke fun at each other, tease about last night’s disaster and let it go. An argument over breakfast is usually over before the plates are cleared, with no grudges on either side.
Bluntness times two
Sagittarius tells the truth in a way that can land like a dropped plate: “Honestly, that outfit’s not your best” or “I never really liked your brother.” Aries has a shorter fuse than Sagittarius expected, and doesn’t enjoy being lectured. Sagittarius does sometimes like to explain the meaning of life to you, right at the moment you wanted to be agreed with.
The quieter issue is that neither of them enjoys staying with something heavy. Grief, a money problem, or a parent getting ill can get treated as something to outrun. Each can assume the other’s fine because they’re both still busy. Months can pass before anyone asks.
Staying when it isn’t fun
Plan the adventures, by all means, then build in some time when nothing’s happening. Sitting at a kitchen table with a hard question counts as an adventure for you two, and it’s the one most worth practicing. Agree on who’s watching the money, because enthusiasm doesn’t pay the rent.
It’s an easy pairing to like and a hard one to take seriously, and the Suns won’t tell you how far it goes. Look at how Saturn falls across your charts, and read Saturn trine Mars to see what a steadier note can do.