Brother the problem is , tefetnalek for the kiss and sex (or teftnalachu with the girls u dated), and relationship will be on rollercoaster so fast that you get bored and lost the meaning and the excitement of that relationship you have with her. Because it was all the Testosterone hormone playing tricks on both ur mind and heart. Then when that level goes down after u have sex. You will be feeling awful feeling (bzw which is normal )but yet cant overcome it because all there is was just emotion and that will make u lose all the interest u had on her. So try to spend time together with the girl u date...go beyond feelings and emotions dont kiss her or have sex with her. Relationship have a hell lot of things to offer other than sex or kiss . So try to experience that first and Just first enjoy the time u will be spending with her. And create attachment in a deeper level. Both in ur mind and heart. So then when ur testosterone level decrease you can overcome that obvious bad feeling and still be interested on her. Hope it helps