Most guys will have pre-cum - it is natural lubrication.
Most pre-cum will have sperm in it.
Pre-cum can get you pregnant.
But sperm has to get inside you, so long as his willy did not get in the way before he covered it, then chances are you are ok.
A lot of guys go a bit soft as a condom is put on, then perk up again, this doesn't mean they have already come.