Either he lost interest, or he just shot his load.
It means you just got bred.
No, he does not shot his load it just goes limp, why is that. seriously.
Could be the smell just got to him.
There could be alot of reasons really,including..stress(even from unrelated situations-job,family,etc),any negative emotions incl;fear,guilt,regret,anger,etc...physical fatigue...or whatever....or basicly anything that can be a distraction.Thats going to happen sometimes with any guy.Also, sometimes us guys will get excited and masturbate,then be unprepared when we get together with our girlfriend.(I've never done that,ha ha)Remember ,men are not like women in preparation for exitement.If we loose our juice then we just aren't going to be very passionate in bed.Tell him that if he spanks his monkey... he'll go blind and his hair will fall out.(and that he's sabotaging his relationship with you).