before marriage is wrong, but what about long-term relationships?

My boyfriend and I have been dating for four years. Our ages are 21 and 20 respectively. We plan on waiting until after college to get married. However, we are of different religions. He is Catholic and I am non-denominational. We both believe that before marriage is against God's word, however, temptation has brought us partake in premarital . We have been having premarital for the past 3 years. For these three years, I have felt guilty every time because I believe in repentance and following God's word on fornication (which is to turn away from sin). I wish my boyfriend felt the same way, but he feels that because we love each other and we will probably end up sinning again anyway, that we should continue. He also believes that we will be decided to enter heaven by our good works, and I agree, but you must follow what God teaches as well. By the way, I only listed our types of religions to give a better understanding of our situation, not to say that one religion is better/believes differently than the other so please do not compare religions. I just want to know what conclusion can we come to in order to solve this dilemma. For now, we have decided to stop having premarital by seeing each other less, but this is proving to be very difficult and ual tensions are high. In a way, it is ruining our relationship because we are more bitter towards each other and bicker more often. To him, having sex in our relationship is as important as not having sex due to religious reasons is to me. What is a good solution for us?