my husband and I separated

My husband and I have been separated for four months. I started seeing someone who quickly told me that he loved me. Though I hesitated, I said it back. Now I'm considering getting back with my husband but I'm about to throw that away so I don't hurt this new guy. What the hell is the matter with me? I've been married a year but my husband and I were together 5 years prior to marrying. I've been seeing this new guy for a month. He's so sweet to me and he's really put his heart out there. I need some advice or just some wise words.