I won with diplo and military in one game now im trying to do science but someone else is aswell can they still win even if i cant (again)?
no, the first victory by any civ, is the "true victory" of the game. Even if you can conquer enemy capitals "one more turn..." after winning first victory. This applies, if all victroy conditions are enabled normally in the beginning of othe game. Score victory, it gives victory automatically to the civ, which has most score (who is score leader) at a certain point in turns, in the game, usually it's quite late game though.
If you were to win score victory (your victory screen is a cool postage stamp!), then that means that at the same time, NO other civ, has been able to win at the same time thru culture, space, dom, diplo. In cases such as these, score victory is awarded to the score leader after certain turns in the late game.
If you quit the game, after you win space victory, you can see that there is no longer the "retire" button in game menu (normally, if you retire from game, you will be defeated from that game, but the option is unavailable at that point after space victory is achieved.)