its normal that when you're trying to put your rod in it will sometimes become soft bcoz u put all your focus into 'putting in' then u cant maintain the 'horny feelings'.. so make it as fast as u can

while its inside and u move it in and out.. it will become hard again.. no worries

and yes too much of porn will make u cannot cum in the real situation. you n the girl might be tired already while you're still stroking yourself hard..