I saw this posted somewhere - saying if you are in love you will not be interested in someone else and if you are interested in someone then you’re not in love.

I agree with this. But my ex always said he knew he loved me and even to this day will try to tell me he know he loves me and we are meant to be and all that. And most of his actions proved he loved me, BUT he was interested in other girls. He didn’t pursue them (that I know of) but he would talk to them more than his other girl friends and would text them sometimes and lie about it and later I found out he said he had crushes on them, for months at a time but said that didn’t mean anything and that he loved me.

Now back to the original question - I believe that if you’re in love you’re not interested in other people. Because I was totally in love and no one else interested me in that way.