So this is Altaïr, he's the first one that Desmond managed to get 'in touch' with through the Animus. He was born in Masyaf, Syria, in 1165, during the Holy Crusade, and at first, he was a reckless, brash, arrogant assassin that had a lot of promise when it came to his talents, but who needed a major wake-up call to become the man he became later on. In fact, it was only when he broke the three tenets of the order during a mission to retrieve an artifact at Solomon's Temple. Stripped of his title of Master Assassin and going back to novice, Altaïr had to go through a lot in order to learn about the life of an Assassin in the Brotherhood, gain the respect of his Brothers and obtain the position of leader and mentor.
Of course, now he's finding himself in modern-day London with no clue where he is, how he got there and more importantly, how does to get back! Not only, he must also figure out what is truly going on, so maybe that will give him the path back home.
Altaïr is a wise man who is also charismatic and a born leader. He considers anyone in the Brotherhood his family, in a way or another. They are a 'Brotherhood' after all. When he manages to figure out that the Brotherhood is still alive in modern days, he will look for it, and he will do his best to integrate himself with them all. But... he can be very private and very cautious with who he actually befriends. That's not to say he wouldn't have them, though. He probably would. And he's actually a very good friend.
Templars, anyone backing the templars up. Basically, he fights for freedom, he has since he became an Assassin. Anyone stopping that would have problems with him. And Altaïr, despite actually having the peculiar habit of giving his targets time to speak before he kills them, he never really stops unless they are indeed innocents or they don't need to die. So he's not a good enemy to have.
Not on his mind right now. He is considered a handsome man and the whole mystery bit about him could make women come to him and while he indeed likes women, he's a serious man who will one day marry, have children and have a family that way. At this point in his life he hasn't met with Maria yet, he has fallen in love with Adha and avenged her death (quite ruthlessly so too). So... very unlikely that he will bother with it in present times (besides... if anything forces him to stay in the present and not go back to meet Maria, get married and have children, Desmond won't exist, since, you know, ancestral and all that... hah!).
Granted, if there WERE a Maria in present times, things could be different. AND MUCH more complicated.