because it is their engagment finger
The right
right
A man can wear his wedding ring on his right hand before marriage. However, when a man or a woman wears a wedding ring on the right hand it frequently means that person is a widower or a widow. Wearing a ring that way could send the wrong message.
right
To show the love and fidelity that you have for your husband/wife.
A married man wears his ring on the left hand.
In North America, it is not customary for the man to wear an engagement ring. However, if a couple decides to break from the norm, the ring is to be worn on the same finger as the female, that being the ring finger of the left hand. In some cultures and in certain parts of the world, the man and/or woman would wear the engagement ring on the ring finger of the right hand and then make the switch after they are officially married.
Wearing a black ring on the middle finger of the right hand is considered a common symbol of asexuality. Some asexuals do wear a ring on the middle finger of the left hand instead. However, the number is very small, so chances are a ring on the middle finger of the left hand is unrelated to asexuality.
There is no reason - he may just like wearing a ring there.
On the left hand ring finger.
Traditionally, the left ring finger is for love while the right ring finger is for pride which is why wedding rings are worn on the left hand while school rings are worn on the right hand. Many gay men wear their commitment rings on the right hand to boycott the tradition of a wedding ring on the left ring finger since many states do not allow same-sex marriages. If you are going to be wearing a commitment ring between partners, many jewelers have different styles to choose from however the style is based on your personal decision.
In the US, a man wears his wedding ring on the ring finger of his left hand. This stems from the belief that people used to have about a vein that ran from the fourth finger directly to the heart. In Orthodox Christian, and some Roman Catholic and Protestant countries the ring is worn on the right hand.