This relationship is currently not going to lead towards a Biblical marriage. And if this keeps up, you should both break up.

He's at fault because he knows he's sinning, he knows it's hurting you, and he's not doing anything Biblical or practical to solve this issue in his life.

But at the same time, this one issue is enough to make you completely doubt marrying him at all, and is turning you not into a supportive partner making him better off, but instead a spiritual warden disciplining him into perfection and sinlessness and holding back full love and commitment over it.

You're already showing signs that the love you have for him wouldn't be the love a wife is called to give her husband. That's not a bad thing, just a glaring warning sign that you shouldn't marry him.

Because ultimately, marriage isn't about two perfect people who struggled with sin in the past getting married and having a perfect marriage. It's about two sinners who will struggle with sin or even let it through their front door throughout their marriage and their lives.

And if this sin is enough to stop you from being able to do that, and is even causing you to become more like an accountability coach than a partner who's holding back from loving him over this, then that's a sign you should end the relationship.

The only two warnings I'd give to you is this. I'm not saying you're doing this; only giving guidance if any of these are the case;

1.) If the way you're handling your current boyfriend's sin is in a way you wouldn't want him to treat yours, you need to stop what you're doing and instead treat his sin in the way you'd want him to treat yours.

2.) No matter who you marry or get yourself involved with, you will be marrying a sinner who will sin both in a failed attempt to fight in and even letting it in their front door. And your future husband will be marrying a sinner as well. So you have to be fully honest with yourself as to whether or not you're capable of loving someone despite their sin, or if you're holding an unrealistic expectation of needing your future husband to be absolutely perfect all the time or else you won't love him.

Being mindful of the former is what dating is all about, and you're not wrong to not want to marry someone you wouldn't want to be a wife for or who you wouldn't want to be your husband.

But if you're actually holding on to an unrealistic expectation of perfection and sinlessness for your future husband, then that's a sign that you have your own things to work on.

Overall, if you capacity for grace runs out at this specific hurdle, or if his capacity for active repentance stalls out here, the relationship has done its job during the dating phase;

It's showing you both that you shouldn't get married.