Stop

Sex shouldn't be what keeps a bf/gf around. If you want to wait until marriage, let the person of interest know that ahead of time. If they claim to understand and later down the line try to persuade you into sex, give a warning. If they still can't respect you and your wishes... end it. It can be so hard to live sex free, especially if you've experienced it before. But be encouraged and know that prayer will go a long way. Because you can't overcome sin alone.