I am in love with my best friend?

I have been friends with him for almost 15 years. I have been married for 4. I got married to the "good on paper" guy. He is a good guy that doesn't smoke, has good credit, blah blah..ya know the things people look for...but the problem is..we are like oil and water. We do not get along period. I found out about a year ago that I was infertile. At that time my husband and I seperated. I was with my best friend and I told him. He comforted me and at that point I knew that I felt more for him than just friends. We confessed our love for each other around that same time. We still hang out but only when my husband is involved of course. I don't know what to do. I know it may be a terrible thing but how do I change how my heart feels? I have tried to use my head my entire life and do things right but my heart is telling me that i love him and not my husband....