I had sex with my ex, was it a mistake?

Long story short, i finally give her the time of day after we had broken up about four months ago. She, on several times, tried to break the ice but i wasnt having it. I just wanted to move on, granted i am still in love with her. So like i said before i finally gave her what she wanted and agreed to speak. She insisted on doing it in person so she offered to come to my house. I reluctantly agreed. We had a conversation for about two hours in which we both spilled our guts out. But we both finalized that maybe its best if we just remained single, although we still hold strong feelings for one another. it just seems that things are just not right for us to work now. We both have alot on our plate but we didnt want to let go of each other. So when things came to a close, i just grabbed her and kissed her, she subtly replied. Than that simple kiss became a passionate one which led way to sex. After sex, we didnt feel weird, in fact it was as if we had never broken up. We laid there for about half an hour just reminiscing our past and laughing like before, but we both were left utterly confused. I really dont know if want to get back with her, but i know that i am still in love with her. Was us having sex a mistake?