It's quite a stretch, fancy being realistic? (8)
I believe the answer is:
lifelike
'realistic?' is the definition.
(similar in meaning)
'it's quite a stretch fancy' is the wordplay.
'it's quite a stretch' becomes 'life' (I can't explain this - if you can you should give a lot more credence to this answer).
'fancy' becomes 'like' (both can mean to find someone attractive).
'life'+'like'='LIFELIKE'
'being' acts as a link.
Can you help me to learn more?
(Other definitions for lifelike that I've seen before include "Exactly like real person or thing" , "Realistic" , "Could be mistaken for the real thing, like figure in wax museum" , "True-to-life" , "Resembling a real person or thing" .)