Yes very much so. Although Kinsey's methods were a little off, the basics are pretty much accepted...sexuality is a spectrum with 100% heterosexual at one end and 100% homosexual at the other end. Some people will be at the further ends...being 100% attracted to one sex or the other, whereas if anyone has any attraction at all, no matter how small to both sexes, then they fit somewhere between 99.99999999% heterosexual to 99.999999999% homosexual. You can guess that means that there are pretty much an infinite number of levels of bisexuality.

That means that even if a "normal" heterosexual man just once watches some gay men having sex and gets aroused, whether he masturbates or not, he has demonstrated that he has some sexual attraction to other men. At least in my opinion, that means that he has some homosexual aspects and that he is at least some % homosexual. That means he isn't 100% heterosexual and therefore falls somewhere on the spectrum as bisexual.

In your case, you have an attraction to women and their breasts, and an attraction strong enough to get you aroused. By my interpretation, this shows you have at least some homosexual aspects within you, therefore you are bisexual, even if only "a little".

Believe me, I know as I too am bisexual, though I'm closer to 60-70% homosexual and 30-40% heterosexual. And I haven't always been at those levels. I was pretty much gay as a teen (90% homosexual), relatively straight through university and my 20's (65% heterosexual) and have moved back the other way as I've gotten married, had kids and gotten older (60-70% homosexual).

I'd avoid worrying about labels. Just live your life being comfortable with who you are. Your inborn attractions (at whatever % they are) will draw you to whoever you will be attracted to in a way that matches to your personality.