I have major issues, I don’t know if I should move on or not.

I have been in love with the same guy for 6 years. We dated for the first three years and have been best friends for the last 3 years. I have been dating someone else for the past three years off and on and lying to myself about my feelings for my ex. My ex, on the other hand, has been wanting to get back together the whole time. I recently decided to quit pushing my feelings to the side and to admit how I feel about my ex. Turns out, he has been dating a girl for the past month and a half without telling me. I ask him if I should move on, but he just says he doesn’t know. He admits that he still loves me and still has romantic feelings for me, but that he is with her now and he needs to finish it so he doesn’t wonder what if. The way he talks, he doesn’t act like he really thinks it is going to last more than a few months. Also that if it ends this summer, he wants me to move in with him and get engaged shortly thereafter. I keep going back and forth on what I should do. Do I trust that six years is more than whatever this girl is and that he just needs to make sure I am the right one given that I made him wait? Do I count my loses and try to move on?