Why you should love yourself:
1. No one cares about you more than you: no one is interested in your life, well-being, safety, health, happiness ... existence, more than you. Don't blame others for their self-interest; it's only natural, logical and healthy. You are self-interested too, even if you think otherwise.
All humanity's interests can be perfectly mutual only if all humans merge into One human, as it had been once in the faraway past when a group of primitive cells merged into One body. For now, we can legitimately, equally reciprocate interest and disinterest, not loving anyone or anything not serving our present and future interests.
If a man finds it unethical to love himself only, he is only blindfolded by a social instinct keeping him from seeing "the truth": that life has other pleasures to enjoy and needs to satisfy, away from people, alone, without fear of being alone.
Social conventions prohibit us from admitting a simple natural truth, fundamental to all healthy interactions: you are the center of the universe, as everyone else is to themselves; in other words, "the world is you." You cannot possess that which moves outside your orbit, beyond your vision and control. It's unworthy of your love because it cannot give a secure pleasure, since you will always live in fear of losing it. Whereas, you cannot suffer losing you, because you cannot lose you, as long as you exist.
Only when others expand or at least reflect your self-love, can you safely love them. It's paradoxical to trust what you don't have, let alone will never have. Loving others should only reflect or originate from self-love. Others-love is more fun IF it adds something new to self-love: new color, shade or light to your ever-changing self-portrait—one you enjoy looking at, not hiding from (like Dorian Gray's).
Love your self only and it will be your lifelong guide. Unlike some think, a self-lover doesn't enjoy killing, harming, or even ignoring others; a self-loather does. You love others more when you see how every human, group, or country can provide you with something you lack. They are the other parts that complete you, as you complete them, making a larger whole, a greater SELF.
For harmony's sake, however, some "distance" is vital betewen you and them, to help each other properly. Look how scientists, philosophers, or scholars are confined in a lab/room to focus and create more for humanity. They live both the present and the future, expanding their self in space and time.
Love is to desire what you enjoyed before or expect to enjoy later. It's a passive unconsummated state of anticipation you feel toward all old and new sources of pleasures. In your case, you were the common source of pleasure in all previous pleasures you had in life, without which (you) no pleasure could have been enjoyed. You are the beautiful "beholder" who make surroundings look beautiful, even when they are not. Thus, love yourself only, without fear, guilt, shame, or hesitance about it:
Once other people find an "alternative" to you, you become forgotten, with pleasure. They won't stop enjoying their life for the sad memory of you. So, appreciate, protect and enjoy your life while you have it; no one will do that for you.
2. No one understands you better than you. You know better the making of you, even if you are not intelligent, educated or versed in psychoanalysis.
Other people understand you partially, with some more than others: psychologists, family members, close friends ... They only see you from outside, from their perspective, without involvement. Your mindset, character, likes, dislikes, genes, memories, upbringing, environment, weakness, strength, failures, successes ... are too complex to understand for someone who doesn't have them altogether, and too many that the combination of which are uniquely YOU. The best psychologist or closest friend can only understand part of you; it's for you to understand the other parts.
Other people understand you temporarily when they put themselves in your shoes, imagining they were you, by the act of sympathy. However, it is only for a short time, as the force of reality wakes them up quickly from imagination, since the former is stronger than the latter. It's hard to give up oneself, one's identity, even temporarily, and become somebody else:
It's a shame to keep asking for others' opinions about you (a known addiction to others' approval). Your choice to be self-ignorant is egregiously manifested when strangers tell you things about you that you didn't know about yourself. You didn't spend enough time with yourself to understand those things that unconsciously transpired out of you until some strangers told you about.
Self-knowledge is acquired by looking inside and outside. Inside knowledge is acquired by spending quality time with oneself: self-talking, self-analyzing, self-encouraging, self-criticizing, etc. Outside knowledge is gained by learning about other people, from books or experience, comparing yourself to others you meet, hear or read about.
If you are restlessly sociable, it's a good exercise to start with understanding and empathizing with others, whom you love being with more than being with yourself, till it gradually helps you understand yourself. You may think of yourself then in the "third person" seeing you with others' eyes, from outside. You must get out of that prison of self to get the whole picture, whether you are alone or with others, by thinking, reading, or socializing, to broaden your mind and think of "you" as "he/she/it." Be temporarily a stranger to yourself, a mystery you can't understand, and prolong that great mystic feeling.
3. No one can help you more than you, because you are always available to you. Just as other people's hearts and minds are not with you, so are their bodies. Nobody may be around for "saving, helping, entertaining ... or talking with you" when you need it most. So learn self-sufficiency skills before you learn social skills. Learn how to do all the above on your own. Personal skills are constantly honed, lasting longer. Social skills are commonly abused (however praised, because it's easy to conform and follow the herd) in deceiving the gullible and manipulating the innocent. Self-love protects the least intelligent against deceivers, liars, and pretenders. If you are "dumb and proud" you can still be amazingly stubborn.
Take care of your self, then: protect it, nurture it, support it, encourage it, console it, comfort it, please it ... enjoy it, before both of you leave this short life. For if you love it, you can easily love other things and people, whose role will only be complementary, adding to the beauty of picture you've been already painting. Self-lovers live long, out-living self-loathers. So, don't follow the latter, who may ask you to join them, to give company to their misery, even when they call you a selfish self-centered narcissist. Don't lend an ear to them. Equally ignore their praise and chiding. Be deaf.
When you love yourself, you will be at no emotional risk of losing a friend, lover or relative, nor living in fear of losing any, someday. Attachment to yourself is safe, because you will always have yourself as long as you breathe. Love yourself to have emotional freedom and mood stability: all the others come and go, except you. They die, travel, get sick ... or just change, personally, physically and mentally. Unlike mourning other people, you won't be around to mourn yourself. Your heart won't be broken, because you won't feel a thing.
4. You avoid the harms of attachment to other people, when you love yourself. You won't act like social addicts who lose their self-control, time, energy, privacy, dignity, honesty, and physical and emotional safety, because of other people.