@Rheeve If the only thing you've ever seen is the stupid oversexed shit that passes for popular culture in recent years, I can understand how you might think that. But in reality, alpha and beta designations have no relation to sex; they are measures of how you conduct yourself under social pressure.
An alpha is someone who maintains personal integrity and attempts to overcome social pressures to accomplish his/her objectives. A beta is someone who knuckles under and does what other people tell him/her to do even when (s)he knows its wrong and/or it violates his/her personal ethics.
This MC bitches eternally about how wrong this is, but still cheats on the woman he "loves". So he's either a serial liar, a coward, or both. Both of which are classic hallmarks of a beta.