Why Do Men Look at Other Women?
What's th real question here? Are you just curious? Or are you worried about losing his commitment. The answer to the explicit question follows immediately. Tips on guaranteeing his commitment follow that.
"Why does my boyfriend look at other girls?"
A. "Because they are attractive."
At greater depth:
The origin of the question shows a concern for your relationship but suggests a misunderstanding of male sexuality.
A man gets pleasure just seeing women. It is a pleasure in and of itself. He doesn't need to think of having sex with her. He certainly doesn't need to fantasize starting a relationship with her. He's not even conscious he's doing it much of the time.
The sight alone brought him pleasure so reliably that within a few weeks of the beginning of puberty, he was firmly conditioned to look. If he didn't look at women, he wouldn't be interested in you either.
My wife knows this, and is happy to point out attractive women to me. ("Over on the bar stool, a split skirt.")
Simply looking at other women is not a threat.
What he is looking at depends on what he imprinted on at the beginning of puberty. In North American Anglo society, he was given ample opportunity to imprint on the breasts, but it is really a matter of chance.
Male sexuality at this level is not personal; it is more than personal. It can be understood as a response to The Feminine. Visually, it is a response to a physical symbol of Woman. Poetically, you might call it worship of The Goddess. And yes, I'm phrasing it in this way in response to the widespread disparagement of male sexuality as crude or dirty.
Tips on guaranteeing his commitment
Since males can respond physically to so many women, they have a great freedom in to whom they choose to commit. When a man commits to you, it is because he wants you, just the way you are, or at least appear to be when he is making the commitment. If you wish to keep his commitment, you need to be and remain that way after he has committed. Commitments must be renewed every day.
What then does he want to commit to? What do you need to be?
He wants you to represent The Feminine for him.
He wants you to be physically attractive; although great beauty is not necessary. The particular physical attributes he finds most attractive depend on his imprinting.
He wants you to have an attractive personality. In most cases, he will want you to exhibit a strong, powerful femininity, what Kara Oh calls "feminine grace," a poise and comfort in being a woman.
He wants you to admire him as himself, which includes his being a man. Berating him for looking at women does not appreciate his being a man. Please understand that if you cannot accept him fully, including as a sexual male, you are risking that he will become attracted to someone else who does.
So it is better not to ask, "Why does my boyfriend look at other women?" It is more productive to ask, "How can I fully admire and love him as he is?"