Fun fact, 99% of the time when a guy says something like "I don't want to get married" what they really mean is "I don't want to get married." You don't have to read between the lines or figure out any deeper meaning. Sure, he could be scared, but if he is you still shouldn't force him. It's nice you love him and want to get married but if he doesn't want to you need to respect this. Maybe he's not ready now, maybe he really doesn't want to ever get married, either way you need accept this. You may love each other but if you can't find a middle ground you may grow to resent each other.
A marriage spell forces him to do what you want, and he will one day regret the marriage because he never really wanted to get married. It's probably not you, he probably doesn't want to marry period. If you feel you need to get married now, talk with him, and be mature enough to walk away. [Please note, I'm not saying one argument you should end things, but if this is something you cannot get over, you might need to walk away]
Marriage spells are better done as a couple to strengthen your bond.