I have one question Maggie...
Do you love him???
YES!! very much so!!
Then, you have a lot less to worry about, if your relationship is genuine, and he feels the same way. Things should turn out better. And also, if you love him, then marry him. It doesn't guarantee that you would have his visa approved, but it certainly increments the chances.
The visitor visa could raise some doubts, but I think my best advice would be... be completely honest about it. If you lie that could hurt you too anyways. Your relationship is true, and your intentions are honest also, there is no reason to lie for that then. If he explains the officer whats going on your relationship, that you are gonna apply later for the PR but that you wanna get married before you move in together
that you are in love and he is not just gonna overstay because you guys wanna do it the right way. That right now you want to make all the arrangements for the wedding, but also, you have to show the IO he is not gonna become illegal once he gets there. Like if he is working, proof that he would come back to work, that he is economically stable and that this relationship is not a way to get out of his country, but rather is genuine love (Im not sure if I agree with love should be the reason why the'd give a persona visa, but anyways), cause thats what they wanna know. Just show the IO your honest intentions and your obvious efforts to make things right, and you should not have to worry about.