I struggle with the last two also. It's scary, because no one in my family or circle of friends has that mentality. It's pretty disheartening when it comes to females. I've never wanted something long term and I think this is part of the reason. When it comes to my guy friends it's no problem.
Let's get one thing straight though my dude. Suicide is 100% completely out of the question. You have so much damn potential, whether things change for you tomorrow or in 10 years. Something as drastic and permanent as suicide is not an appropriate response. I've been there before, and fast forward a few years and I absolutely can't believe it was even a consideration. I GUARANTEE you will have the same sentiment soon, which I why I urge you to dig deep. Acknowledge how you're feeling and make small steps to better your situation and mindset.
What's a typical day like for you?
Like others have said, little things make a HUGE difference:
-going for a walk/hike
-yoga
-pleasant music (I like the Pandora channel: Movie scores)
-eating more produce, cutting out fast food
-getting a new hobby like playing chess online or photography
-volunteering with the less fortunate or disabled, etc (this will open your eyes)
-reading a book with a positive message (The Alchemist, Tuesdays with Morrie, The Last Lecture)
-join an in-person group/club with similar interests
I hear you in regards to females. I have little trouble getting along with women and many have shown interest but if any feelings outside of a mutual friendzone come up from either or both sides, the more I want to run away. I have gone out of my way to do some ridiculous things to scare women off in the past. I'm talking like, purposely waiting a long time to get her number, straight up telling her stuff like "I don't really deal with people like that, I keep to myself," saying self-deprecating and pessimistic things, telling her I usually cut females off within months, shooting down invites to places etc.
If something along the lines of those examples won't push her away, bringing up my mental illness usually will. If not, then I'll just cut her off myself before or right after it comes to that (mentioning my "real" problems) because I feel people are better off without me to begin with so I'm doing us both a favor by avoiding any drama. If THAT doesn't work, then I'll just push away anyways because I would rather suffer alone than to tell people about my problems. I've legitimately tried changing my ways like with one of the more recent women I've dealt with, but old behavior still comes up. Therefore, any attractive single female I click with usually lasts 4-10 months before everything goes sour. The ones who I've maintained anything with are in relationships with other dudes and/or we're just not interested in each other outside of a mutual friendzone.
Besides, like I said a part of me wants to die by 30 so I often feel that I shouldn't live like someone who sees a big future. I'ma be dead within 5 years (at least, I hope so), so sometimes I ask why I should even bother helping the side of me that's actually sociable and enjoys being around people. I usually have too much pride to go the "easy route" but with suicide that goes out the window. Anyone can call me a coward for wanting to die and quit because that doesn't matter when I'm dead and no longer have to live life.
To your second part: Ironically, I'm a psychology undergrad student and I'm not taking summer classes. I want to take a break until winter 2018 so my days consist of looking for work on top of the usual gym and appointments. My hobbies are basically hip-hop, gaming, and exercise and I do more of that when not in school. During the semester, my life is basically just going to classes, working a gym schedule around it (3-5 days/week, routine) and studying. As far as diet, I'm pretty strict most of the time. I've been eating vegan for almost two years, I have a written down meal plan with calculated macros, I schedule cheat meals which usually consist of the same things so I rarely go too far off track etc. No matter what though, I usually spend most of my free time alone and turn down invites from both male and female friends.
The loneliness can be really tough, but at the end of the day I can say: I didn't hurt anyone, no one hurt me, and only I can hurt myself.