Trying to guess what star sign he is based on his "stubbornness" is not such a good idea.
Taurus, Leo, Aquarius, Capricorn, and sometimes even Aries can be stubborn and these signs share this trait but all have different elements.
I have my own way of identifying the different types which seems pretty accurate. Shadowx, pick the one of out these descriptions that sound most like you and tell me if you are that sign.
Aries - Social, Energetic, can be aggressive when being stubborn
Aquarius - Cool and distant personality. The type of person that when you talk to them you think they don't care but later you find out that they've given what you said deep thought. These people are stubborn because they think the know everything and this can also lead to acting conceited.
July Leo - Mentally egotistic, may be shy/quiet to protect against anyone who may criticize. Very sensitive and giving. Even if quiet, they will attract attention without meaning to.
August Leo -Wild, egotistic and lets it show, talks a lot and have a lot of friends. Not afraid to take risks and may be blinded by their self-centered behavior.
Pisces -In their own little world. Not necessarily shy but often quiet in observance or daydreaming. These people are more likely to be drawn to psychic stuff
Capricorn - Negative people who like feeling sorry for themselves and have hope that maybe one day life will get better and they will climb their way up to the top. [Expect LOTS of Cheating in a Capricorn-Taurus relationship]
Taurus - More likely to be gold diggers. Materialistic people who love their money and worry about their weight but loves their food. These are the parents who are most likely to set aside money for their children for future plans like college. For a Taurus, love is communicated on how much you buy for them, they love presents.
If you are with a Taurus, expect the relationship to go down hill if you have unequal rules or you're caught cheating. Taurus themselves are more likely to cheat, however.
Scorpios - I have never met a nice Scorpio before. They are worst than Leos. They manipulate to get whatever they want and they will try to get to know you without letting you know about them. They are also very sexual people. They can hold a conversation about sex and they don't care where they are. These people will have a good ability of communicating with the dead if they train a little.