1. You are putting out the wrong vibe.
Women are rarely capable of entirely separating emotions from sex. If you’re having regular sex with someone, chances are they are on your mind some of the time. Whether those thoughts are positive or negative is irrelevant. The bottom line is that you are preoccupied.
Human beings are capable of almost limitless facial expressions and cues. Many are so subtle they are not registered consciously by the viewer. Still, they create definitive impressions. I believe that if you are having a sexual relationship with someone, it is impossible for you to send the full range of cues that signal interest and availability. By definition, any attraction you feel or encouragement you provide to another man will be compromised.
2. You are not pursuing your strategic objective.
I know several women who dated like it was their job until they found their partners. Often we must take action to get what we want. It feels better and is far more effective than passively waiting for the right person to miraculously cross our path and pursue us. One of the most common ways that people meet their life partner is through friends of friends (after school and work). It should be obvious then that your goal should be to have as many friends and acquaintances as possible, and to consistently make an effort to meet new people of both sexes.
If you are at a party texting your FWB, you are not noticing and introducing yourself to someone new. You are not networking. Even worse, you may decide to skip the party and stay home to have sex instead.
There is also the probable risk of misinformation. Your friends will in some way consider you “taken.” If someone new and interesting asks about you, they are likely to be told that you have some “thing” going on with so-and-so.
These are just two examples of how a casual involvement can sabotage your efforts to get into a relationship, but the possibilities are endless.
3. You are communicating low standards.
It’s no secret that a FWB is a hell of a lot easier to come by than a boyfriend. If your goal is a relationship, then having casual sex means settling for something substandard. It conveys a low opinion of your own worth. It also reduces the pool of potential partners, as many men will prefer a minimum of previous partners to a plethora of previous hookups.
Neither happy nor unhappy, neither loved nor despised, neither committed nor free.
Halfwaying it keeps you single.