Ever since the 1970s, studies have been done on the relationship between sexual activity and testosterone, with some studies showing that having lots of sex increased it while others didn't. Recently, another study was made, with the following results:
Across human societies, males have greater interest in uncommitted sex (more unrestricted socio-sexuality) than do females. A recent study found a negative feedback between men's testosterone levels, socio-sexual psychology, and sexual partner number. Specifically, a man’s number of sexual partners is negatively related his testosterone level, i.e. the more sexual partners, the lower the testosterone level. This suggests that testosterone drives “sexual hunting” in men, but is inhibited when the desires are fulfilled. Thus, testosterone promotes sexual intercourse success, which in turn down-regulates testosterone production. Thus, running around too much may backfire.
In other words, yes, having sex will make a man more masculine, but only with his own wife, or at least, a long-term partner. Chasing sluts will ultimately turn him into this dreaded nu-male type. The funny thing is that before the movie James Bond came along men spending all their free time running after girls weren't considered particularly masculine or worthy of respect.
Men were supposed to do better things with their life than getting easy sex. While it was often tolerated if a man had a mistress, only the lowest classes used the services of prostitutes regularly. And there was no glamour at all attached to "ruining good girls". In fact, there was a good chance her family would kill him or at least, force into marriage which used to be a permanent arrangement.
As the science now reveals, there was a sound reason for this. You can't win a war with an army of soy boys:)
For the reference, this article.
P.S. I should add that a really masculine man does project this aura of being able to get any woman he wishes, because he is highly desirable, in the same way a beautiful female is desirable to men. However, it appears that just like with women, if he acts too much on these impulses, promiscuous behaviour will hurt him in the long run. One night stands ruin both sexes since we are meant to pair-bond.