If you tolerate what they're doing is not good just in the name of love, then you’re making yourself suffered. And it is not loving, after all, it’s dying. Upgrow. Let the truth set you free.
We don’t know what our tomorrow may bring forth. But, I’m believing that when you truly love the person you loved, then it is not an issue that he/she will leave you in the end. Not all first love will stay forever. It’s rare that your first love will go further together in a long run. What makes love to worth spending an entire life, is when you have the faith and trust in the person that God is giving for you.