For the time being, you should respect her wishes. Did she she say why she felt smothered? Are you jealous or possessive? You did not why she feels this way. If so, this is part of your personality, and it will be difficult to change. She is right in thinking that after a little time it would be the same problem again. The words "I have changed" often don't mean much, because in some areas, people don't/can't change.
If you feel that you have really changed, then start slowly; you will have to show her you have changed but it will take time. Maybe just conversations or a meal together. However, if she has made up her mind to move on, there is nothing that you can do.
Unfortunately, loving each other is not enough to maintain a good relationship.