Why does everyone I meet want to kill me? Why can't we be friends?

I don't think you can make an ally or ceasefire when it is 1 v 1. Even in larger games unless you set the allied victory conditions to allow more than one player to win, the AI will declare war on you when you are the last one left. Though why would you want a ceasefire in 1 v 1? Wouldn't it be better to disable the AI player entirely making you the only one in the system?

Well it would make things easier if I made a pact or treaty or even friendship, so I can colonize and build an almighty fleet.

Then execute order sixty-six.

imo its kind of ridiculous how easily the ai a)places so much importance on missions and b)becomes friendly with you so easily, in late game with a at least 3 other factions i usually end up at peace with all except one, who i defeat, simply by getting the first 2 or 3 relationship uprades and not attacking them, which is pretty easy since theyre far away

if i fail a mission because i wasn't paying attention and its too late to reject it, my relationship with the ai who offered the mission drops 2-4 points (or more), even if its to attack my trusted ally who i have 10+ relationship with

I don't bother with diplomacy at all other than to accept treaties when offered. I am in a 10 player ffa now and 4 r dead which I killed 3. Now every race has offered me peace and I accept. Build star bases on all there important planets then order 66 on whom ever is least happy with me. 

The AI will not make alliances in a 1v1, but it's actually very easy to make friends with them in larger scenarios.  You can make AI's very happy by completing missions (usually involving killing another AI's units) and after two or three missions they will make peace.

If you don't like the mission system (like aaa11) you can play with locked teams.  This is how multiplayer is usually played, where teams are set in stone.  You can still form pacts with your allies, but the allies you get are determined at the start of the game and can never change.

With Diplomacy, it has become a lot easier to gain allies through military operations. Unless I'm mistaken, the maximum relationship that one can get under "Military Actions" is 20, so simply pounding one or two AIs to nothing will often make most of the others quite happy with you.

I was playing an 8 player FFA and six of the AIs gave me missions to kill this one other AI.  So I knocked him out in 20-30 minutes and everyone else offered peace treaties