Man, thats a tough question. From 16-28ish I had a rather dim view on long term relationships for exactly the reasons you listed. I mean, why have one when you can have a new ones almost at will? Back then I rarely ended the night alone. The thrill of locking eyes across a bar, approaching her, landing her, it was intoxicating to me. The chase was almost better then the kill, so to speak.
Now I have to agree with Hurlshot. Im all old and stuff now and its very comforting to have someone there for you, sharing interests and goals, to grow old with, to love. We have an eight year old daughter whose the light of our lives and all is good. That doesnt mean I dont occasionally think about that 20-something hottie I just saw but in the end cheating is never worth it.