Aries - independent and passionate. They can not stand the situations, when they were patronized too much, and when their little weaknesses and failures become obvious to the others.
However, they are jealous, hot-tempered and can fall into a rage (though quickly passing). To Aries (best being embarrassed and with the sense of his own guilt) proposed to separate himself, in any case DO NOT tell him, that you felt in love with someone else, or that he - Aries - is no longer satisfying you as a sexual partner, or that you no longer wish to suffer him messing around, not able to provide you with a normal life. This will provoke a scandal (including the use of physical force), and you'll not only be able to leave peacefully, but also end up being his "enemy number one".
It would be all much easier, if you "suddenly" lost interest in the "Napoleon's" plans of your Aries and the same "suddenly" got extremely busy with his health. Drag him to different doctors, feed him with various medicines, complain to everyone about his failing health, make him wear warm socks (better do it in front of his friends) and deliberately obstruct the air vents.
In the same time, it is good if you will find one of his friends telling him, that Aries is a "real men" and praising his strong-willed qualities. Tired of your custody, Aries certainly will grab his "soul mate" and ... will give you a divorce with pleasure.