Antonym search for expanding search terms
That's an interesting problem.

This according to me is the most comprehensive way(if speed is not a problem. Or you can just pull all these words and create a dictionary/database of your own).

You can this , 
https://wordsapiv1.p.mashape.com/words/love/antonyms (More info about this API at this link)

However, you can restrict results to antonyms with this api. 

You can use requests to make API calls. 

import requests
import simplejson
response = requests.get(url)
result = simplejson.loads(response)


Then search for the antonyms from the result. If you are getting a big list of antonyms, use only the top n results for your searching. 

Although, W2V gives most commonly used words in the context of the keyword, it's hard to guess which is the antonym of the keyword.