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If this is soon after your break up, chances are he's on a rebound with this new lookalike.
Now assess if the reason you feel the need to talk to him is because you're feeling lonely or you do still have feelings for him and you think if you retry at the relationship it wwill most likely work, whatever the reason you broke up with him for.
Because if not then try to avoid him but ofc the odd polite text might not be too bad but if you don't rink there's a future for you two try keep contact to a minimal whilst you both heel and you'll probably be able to find someone better than him that won't make you lonely anymore.