I think ROCKAROLLA is 100% correct.
How common it is today to be married or getting married before we've realized any of our potential. The longer you remain uncommitted, the more opportunities will be available to you. It's been stated by wiser Men than I that women are dream-killers - and while I agree with this, I'd say this is due more to the man involved, and their own complicity and apathy, than some grand scheme of women.
It's actually in women's best interest that you don't commit to them for a variety of reasons. I realize how counterintuitive that reads, but in your being so readily available you decrease your value as a commodity to them. Scarcity increases value, and particularly when the reason for that scarcity is something that serves another's interest (hers in this example). The mid-20s Man pursuing his ambition to become an attorney in law school or the pre-med intern spending long hours at the hospital with aspirations of becoming a doctor is hindered and encumbered with the complications that maintaining a monogamous relationship necessitates of him. His time and efforts need to be applied toward acheiving his goals to become an even higher value Man - not just in terms of financial success but for his own edification and confidence. Needless to say, the constraints and obligations that maintaining a monogamous relationship require - both in time and emotional investment - make achieving these ambitions far more difficult.
I tend to promote the idea that Men should be sexually and emotionally non-exclusive until age 30, but this is a minimal suggestion. I think 35 may even serve better for Men. The importance being that as a Man ages and matures in his career, his ambitions and passions, his personality, his ability to better judge character, his overall understanding of behavior and motivations, etc. he becomes more valuable to the most desirable women and therefore enjoys better opportunity in this respect. Women's sexual value decreases as they age and the balance tips into the older Man's favor. It's the Men who realize this early and understand that bettering themselves in the now will pay off better in the future while still enjoying (and learning from) the opportunities that come from being non-exclusive and non-commital make him a Man that women will compete for in the long term.
In your mid-20s you are at the apex of your potential with regards to the direction you will influence your life to go. I'm not going to make any friends by pointing this out, but what pisses off most "serial monogamists" is the unspoken regret of having assumed the responsibilities, liabilities and accountability of what monogamy demands before they truly understood their potential.
Women should only ever be a compliment to a man's life, never the focus of it.