What can I do about a bad night?

Look my life is great. I have a motorcycle , I just got cleared to enlist in the marine corps, I have a good job, I'm at the perfect age of 17 , everything is great. But I have a night every now and then where I feel like no matter what I do there will never be anyone to fall back on. All I have is a small family but I can't pressure them with just a bad feeling . I want to be loved but I can't let myself be loved. I got hurt by the girl I would have died for a long time ago and I haven't let people love me since! Why am I this way and what can I do about it?