Should I follow my heart in this situation?

A week before my college graduation & after coming in and out of my life for months, my bf of a year broke up with me. Only explaining that he was very busy and wanted to be fair to me. He wanted to stay “friends.” I lost contact with him. Four months later & he is texting me. I finally gave him a chance and we hung out yesterday evening. All the feelings came rushing back; there was that magnetic chemistry/attraction. The scary thing is that I am currently in a relationship with a man that treats me the way I should be treated. However, that instantaneous “spark” is not as present with this current guy. Sometimes I feel as if I am forcing my current relationship. What is happening? What should I do?