I'm not discounting your feelings or situation, but dude... you're twenty-eight years old!
The first 18 or so, you lived your life according to other people's rules, standards, and goals.
Then you went to college (probably) for 4 years or so (probably), so you have had six whole years of being a real person.
Cut yourself some slack, man! :-)
I'm 20 years ahead of you, don't know you from Adam, and don't know anything about your situation beyond what you have posted here. So I am totally qualified to give you advice! So here we go...
What I see in your post is someone who isn't comfortable with himself. You aren't connected to YOU. You haven't spent a lot of time alone. You haven't done a lot of introspection. You don't really know what your internal drivers are.
At 28 I was ending my first marriage, working a high-paying job in the tech industry, riding my motorcycle to work every day, living in the Haight-Ashbury, and kind of a wild man. My life was full of noise and action and activity and busy-ness.
It took me about 10 more years to slow down enough and let the dust settle enough to realized that I was afraid of being alone. I had no identity outside of the work I did. I could not just sit alone and read a book, or be quiet, or just sit in the forest and stare at trees. I had to be DOING SOMETHING to always keep me distracted from the fact that I didn't really have an identity.
I didn't know who I was.
Therefore, I didn't know what value I could be to someone else, and that made me a bad partner in a long string of short relationships. Lots of frustrated women who could see my potential, but couldn't help me get comfortable with myself... so I'd eventually slip away.
My Advice: Here's what I suggest: Sign up for a yoga class, and commit to doing it for 6 months. Sounds weird, I know. But you are young and fit. The best way to remain in shape, and in tune, is to do yoga regularly. It helps you keep flexible (and you have NO IDEA how important this is going to be later on in life!!!), it keeps a strong core, it helps you find physical and mental balance, it gives you some quiet time to be alone with yourself and your muscles and your body, and it mellows you out. You can also do it anywhere, at any time, for stress relief, or stretching getting off a long plane flight, or whatever. Yoga is magic and everyone should do it.
By doing yoga, you will be focusing on yourself in a healthy way, spending quiet time alone in your head without family or digital distractions, and you will get to lean more about your physical self, as well as your cerebral self. When your mind has time, permission, and space, to wander... you never know what you might find in there!
Yoga is also a community. A healthy community that cares about each other. And hugs one another. And shares honest feelings. These are things you are missing, as well.
It's not a cure-all panacea, or anything like that. But I think it might help someone in exactly your situation... and lead to long-term health benefits that you will be VERY grateful for later in life!