I kind of get how you're feeling, I've got a similar problem, except this guy isn't my ex, the problem for me is his age, he's... a few years older. I've realised that I can't get what I want and be smart at the same time, so I'm trying to be somewhere in between, but I know that there will come a day when I have to explain that we cant get that serious, and that day is gonna have to come soon.
And just like you I decided that I like being single, relationships isn't for me, I like being free...
And now about advices, I suck at giving them, so they will probably not help you much. All I can say is you gotta decide if you're gonna go with your feelings or be smart, cause, unfortunately, it seems like you can't be both...
Don't fear death, fear the unlived life.