Do you have to change anything when you're single and hating it? There's an old saw about marriage. Men get married thinking their wives will never change, while women get married thinking they can change their husbands. I have no idea how this is supposed to work in non-traditional, non-hetero-normative marriages. What I can say is that being in an established relationship in no way stops the process of change, from both internal and external pressures. Might as well get a head start on it while you don't have to take input from anyone else.
"I'll still be the same person." This is a top concern for people with a fixed mindset. I'll consider changing my attitude at work/getting organized/losing weight at some future point, but only as long as I'm still the same person when I'm done. What I want to know is, why on earth would I want Future Self to be exactly like Past Self? What past age was I supposed to get stuck at? Am I supposed to stay as weepy and inclined to write poetry with a purple felt tip pen as I was at age 14? Am I supposed to be as bad a cook as I was at 18? Is it a requirement that I keep managing money as badly as I did at age 22? Should I have the same attitude at age 70 that I had at 35?
What's the point of aging then?
Getting older but not wiser is the path of pain. Repeat the same mistakes over and over again so you can live the same consequences as many times as possible. Be self-absorbed. Resist feedback from all sources. Always put yourself first, except when it comes to making choices that lead to better conditions for Future Self. At the end of the game, it's easy to wind up broke, ill, and lonely, even then not realizing that change is the solution. It always was and it will always be. Change is what we do with the power of free will.
Change doesn't even require free will. A wild animal will move away from negative situations without giving it a second thought. A wild animal will eat biologically appropriate foods and maintain peak physical fitness, because those are survival traits. A wild animal cultivates social bonds, because that is also a survival trait. They accept and reject potential mates based on... something? They focus on earning a livelihood from the moment they wake up. In a sense, they're organized; either their lives are effective or they're not alive for long. If only I could be as perfect as a worm or a bluebird for one day.
So what do we change and what do we not change? The ultimate goal is to be the best version of you. If that's a snarky, sarcastic you in jeans and a t-shirt, so be it. Keep going until you are satisfied with yourself. The corollary to that is to be satisfied with the Right Things. Does it hurt other people's feelings, infringe on their personal bubbles, or annoy them? Quit doing it. That has nothing to do with romance or dating, but it will affect your chances. Make it easy for people to spend time with you, or, if that's too much to ask, at least convince yourself that it's worth making the effort for one particular person.
Married people annoy one another all the time. We refuse to go to bed at the same time, and then make a bunch of noise while our long-suffering partner is trying to sleep. We insist on hashing out arguments at bedtime or later. We make messes, leave them there, and then get all snotty when it's brought to our attention. We nag. We refuse to apologize. We spend money in secret and we eat the last of the pie without sharing. We put on the ring without any sense that we should try to be good roommates. The First Law of Marriage is that you are precisely as annoying as your partner, only in a slightly different way. Changing yourself first is the only way to nudge your partner into changing, and even then, it's almost guaranteed not to work. The only possible change is self-change.
That's why it's best to change as much as possible before marrying. That way, the person you meet will be at your level, the highest level of which you are both capable. Improving after marriage is making yourself incompatible with your old love. I've seen long-term marriages capsize many times over this. One partner gets fit, gets an advanced education, starts making significantly more money, develops an artistic skill, or whatever. The other partner doesn't change at all. Even though one person is now theoretically more attractive and interesting, boom, divorce. Now we have to add to the plan: change as much as possible before marrying, and marry someone who also is dedicated to growing and improving.
There are many comforts to long-term love. Inside jokes. You can almost read one another's mind and speak in shorthand. You can order for each other in restaurants and you know how to cook each other's favorite meals. You can give each other massages correctly. You can take care of each other when you're ill, which is usually out of sync by a couple of days. Someone is generally on your side. The most valuable thing a mate has to offer is the capacity to notice and tell you when you're off track somehow. We call each other out on our BS. We shore up each other's confidence and remind each other of our best selves, sure. Those are good things, too. But everyone really needs a truth mirror, and a long-term romance is probably the one with the clearest surface and the best lighting.
My husband and I started changing each other before we started dating, before any romantic feelings even developed. I talked him into saving more in his retirement account. He taught me how to get better at shifting gears in my car. I convinced him to switch from iceberg lettuce to darker greens. He talked me into getting rid of my storage unit. Since we met, we've lost a combined total of over fifty pounds. The more we changed, the more attractive we became to one another. One day, we realized it would be foolhardy to ever let each other go. How would either of us ever know how far we could go without the other's counsel and support?
Most things don't require change at all. Listen to whatever music you want. Wear whatever you want. Read whatever you want. Make friends with and hang out with whomever you want. Make your own decisions about your career arc, your personal electronics, your fitness plan, whatever. You still get to have your favorite color and vote your own way when you're dating. Where it helps to change is in how we communicate, what moods we tolerate in ourselves, what attitudes we cultivate, and whether we take responsibility for our own lives. Still yourself, just the self that is easier to get along with.
I've been working with chronic disorganization, squalor, and hoarding for over 20 years. I'm also a marathon runner who was diagnosed with fibromyalgia and thyroid disease 17 years ago.