I think it's perfectly acceptable to propose to him, if you feel that strongly about marrying him. I'd take it as a compliment if a woman proposed to me...(but I don't know if every man would see it that way, or not ?)
You could try dropping some hints or something first, and see how he responds.
Do you think he's ready for marriage ? Have the two of you ever talked about it before ?
You know him better than anyone, so you have to use your judgement on whether you think he's ready & whether or not you should propose.
If you do decide to propose...then I'd take him out somewhere (to his favorite place or doing his favorite hobby/pasttime....and do it there.
Let us know how it goes....wishin' you good luck, with whatever decision you make !!!
