If you choice 而加既男朋友,一起已去到可以談婚論嫁既地步.
However, you complain that he is 好唔成熟,脾氣又差,又唔錫我,唔愛我,從來唔會就我的. That means you don't love him!!! Also, you don't believe him (as you said 之所以還同我係埋一起,是因為佢自覺年紀唔細,而我又對佢好,怕分了手找不到更好)
Also, as you still consider should you marry him or marry the other man now (已去到可以談婚論嫁既地步. => I am 100% you don't love him!
Even you marry him now, you two may 離婚 after a few years, if you find your Mr. Right.
For 另一個男仔,係追左我成8年,話會等我,時常都話想同我結婚生仔,對我好到不得了...
For those 'group' of man, he 追 you 8年 even he know that you have a stable +可以談婚論嫁既 boyfriends. i.e. He thinks that when love comes, even the girl have bf/husband, a third person is correct. He just care who will win the game finally..... I don't think those type of man (third person) will be a good husband + father.
Do you sure you will as beauty as you are now 30-50 years later after give birth of some kids? At that moment, he may find a second wife / gf ............... as he is a third person now, he will fall in love with other third person easily (as they are similiar people)
i.e.finally, the result may be the same => 離婚