Basically I Have A Problem! For Sum Reason I Cant Stay Commitied in a Relationship!?

Like within 3 months i would get sick of the gerl and wind up Leavin Her! My longest relationship was only 3 Months &nd im 20 yrs old Has any1 eva had that problem and how can i stay commitied &nd Change my datin Problem? p.s i am currently Talkin to sum1 @ da moment that i really like but i dont wanna blow it soo please help