good to know that you're moving on
I'm not really a good one to advice when it comes to men, my past relationships were all a mess. Though I have myself to blame too. But I've learned my lesson that never assume something and dont expect something when it comes to men. I guess we tend to put meanings to their actions toward us, but from their point it was nothing special. The best way to know if you have doubts and questions, is to ask directly and frankly. Expect to hear something from them you might not like to hear, most men are frank, dont beat around the bush.
When a man says 'let's just be friends', take it as it is. Even if he is confused what he really wanted, treating him as friends will give him the space he needs. Time can only tell if you are meant to be friends or more than friends.
About for a man to have a changeable mind, you'll be surprised how men can change their mind overnight. It's not really about being a man or a woman how a person can change her/his mind easily. It's our right to change our mind especially if we're not too sure of the result or the outcome of our decision. Though having a very changeable mind can make a person unreliable.