Nostalgic means there are things cause you to think affectionately about the past. Sentimental means someone produced emotions such as pity, romantic love or sadness, which may be too strong or not appropriate.

Being nostalgic is thinking back (usually fondly) to earlier times. When you're sentimental about something, it's because it means a lot to you emotionally. A vase might have sentimental value because of the memories that you associate with it - perhaps someone special gave it to you. Does that help?