Thats it. That's all you need to do. Just keep her your girlfriend, don't let her move in, and have sex regularly with her. You get to have sex with your girlfriend regularly, but you won't ever actually commit or marry her. Of course, you wouldn't disclose this at all since you need to protect yourself, but if at any time she gets angry about commitment just dump her and find a new girlfriend.

All the while just focus on your career and net worth making yourself an even more valuable BB man to other women, making the replacement process all the more easy. I can't see any downside to avoiding marriage for a BB male. It's all upside.