With two such charming and flirtatious signs coming together, there's another big problem: both tend to struggle with monogamy and being with the same person for many years. It's not uncommon for Gemini and Sagittarius to prefer having multiple lovers. If they have a talk and work out an arrangement, such as an open relationship, they could really be a power couple. But social norms and jealousy may stop them.
Both of these exciting signs crave new adventures, the unknown, and spontaneity in their lives. This is all good and well, but it can mean that they don't commit to anything for long, including each other. With both of them excited about new projects (and people!), it's easy for the relationship to simply fall apart. Hey, at least it's not a messy break up, they usually both agree.