In my experience it is very common for the person who is the least emotionally tied to the relationship to be quite happy to stay friends. I think and this is just my opinion, that there are some men who are content for a relationship to 'jog along' even if they don't want to commit and aren't convinced this person is 'the one'. If you allow this to happen, it may be even more painful when at some time he meets someone and falls for them. He must let go and allow you to get on with your life. And, no you are not being extremeist, you are following your interest to protect yourself.
Just because you have initiated the ending doesn't mean that you are the one who hurts least.. I suspect in your case it's the opposite. Your emotional attachment seems to have been so strong to this man that it is indeed painful for you to continue to see him under different circumstances. Sometimes people just don't realise how much pain we feel when we have to initiate a break up even though we don't want to.
It's possible that he feels that because you initiated the end, you may well have worked your way out of the emotional attachment and are ready to just be friends. I think he is short sighted and hasn't thought this through. He needs to understand that the one who ends a relationship is not always the one who feels least pain.
When you break up like this you need time to grieve, time to be alone and time to let go of the sadness and pain and slowly rebuild your life to welcome in all the wonders that are out there waiting for you. As long as he is in your life you will find it difficult not to hope and as a result, you will be unable to devote your energy to moving on and opening up to new love.
I suggest you firmly tell him that at the moment, painful as it is, you need him to understand and help you and the way he can do this is by letting you go. Tell him that you haven't ruled out the possibility of friendship in the future but you can only enjoy that kind of relationship when you have got over the very strong pain and grief you are obviously feeling right now and that if he isn't prepared to offer you the support and commitment you need he must let you be free to find it elsewhere.
If he truly wants to be friends, is a good person and isn't just being selfish and hoping to have the good things he got from your relationship without any commitment, then he will understand and want you to find the happiness you deserve. A true mark of his desire to be friends is to be able to let you go.