My ex, it wasn't a straightforward relationship, but when we were in love I have never felt a connection like it, I adored him and when we spent time together it was like we were in a bubble and the real world faded. We fit together physically and mentally like I haven't experienced ever.
He turned out to have some significant secrets though, I accepted these and even encouraged a bit, but he was a liar and the relationship ended in a tumultuous way. We dragged it out, but it wasn't the same. I still to this day don't know if he truly loved me, or was just playing a game.
That relationship truly trashed my mental health, but I have almost let go of the wondering. It doesn't matter if it was real for him, it was for me and that is what counts.
It's hard though, because I can't imagine having that connection with another, not even sure I would want to, it was very intense.