Sadly, the feeling of disgust when a guy starts to like you is the consequence of a negative experience from a previous relationship that impacted you emotionally, psychologically, and viscerally.
Whether it be a previous relationship, or guys you have encountered in your life as a whole, there is emotional angst within you.
There is a facet to your history that has made you look at guys, and yourself, negatively.
Look back on your life.
Somewhere in your past is an experience that has affected your outlook on life and relationships.
A girl who is already in a relationship with someone else wants to strictly hang out with you in a group capacity.
She wants to be there in a group of her friends, or in a group of your friends, whenever she is around you.
In essence, she doesn’t want to be with you on a one and one basis.
Be observant.
When she consistently tells you that she will show up with her friends, after you invite her to a one on one activity, she is already in a relationship or isn’t interested in you.
In coming off as though he is all about himself and incapable of thinking about the well-being of someone else, a girl is less inclined to get involved with him.
Know the difference between being legitimately confident and being conceited.
Whether it be a previous relationship, or guys you have encountered in your life as a whole, there is emotional angst within you. 
You were so caught up in his looks or in how he made you feel. 
She wants to be there in a group of her friends, or in a group of your friends, whenever she is around you.
She does this when she thinks her boyfriend isn’t giving her the attention and appreciation she feels that she deserves.
A guy