I think your both bf took you on ride and left you once got satisfied. By heart of heart you also know this and you feel guilty about it. Because of this guilt you have negative tone about your future relationship. This is usually what happens to girls who are involved sexually in noncommittal relationships. Now that you have realized, try to overcome the guilt. Accept it as your fate and immaturity. Look foreword with positive tone. Do not live in past and prepare yourself for future.