Guilt have always been part of sex, first of all, out of religion, sex gives guilt because with time and energy that is invested in thinking about sex, a person can devote that time and energy to other activities , Develop, study, what is known in psychoanalysis as "the sublimation of libido"
It's better to forget about sex and think about love. Sex is temporary, love has more dignity, more eternity, just look at Jesus, who love all humanity and today billions of people love it
I do not know what to tell you, It is very understandable that at your age you want to experiment with women and have relationships. But it is necessary that these relationships have as pillars,the love, respect, dialogue
You have to be a friend of your girlfriend, you have to be a companion who cares for her, protects her, and listens to her
Otherwise if you see a girl and only want to satisfy your sexual desires, it is inevitable that sooner or later you feel guilty for that, because in addition the woman would feel used, insulted.
For that reason, it is necessary to be honest, to be a good boy, and if you go out with a girl, take care of her, be faithful to her and follow these guidelines you can enjoy intimacy without feeling guilty
One more tip, use contraceptive methods if you still have no plans to be a parent, because much more guilt can be felt when having a child, not wanting it but for an oversight having relationships.