This is a conclusion, not an observation
Worth separating those two things immediately, because everything else follows from it.
What you actually observed is something like this: nobody invited you to the thing. Nobody texts first. Conversations are pleasant and end. You left a party and no one noticed you had gone. Those are real observations and they probably happened.
"Nobody likes me" is not an observation. It is the explanation your mind attached to them, and it is the one explanation that requires nothing further from you except to feel bad. It also has a serious flaw, which is that it does not survive contact with how adult social life actually works.
Why the evidence you have does not prove what you think it proves
Here is the part that reframes most of it. In adult life, almost nobody pursues anybody.
The people you are measuring yourself against are not being sought out either. Your coworker who seems socially fine is also not being invited to things. The neighbor with the busy-looking life is also waiting for someone else to suggest a plan. Adults have almost universally stopped initiating, because everyone is tired, everyone assumes everyone else is busy, and everyone is quietly worried about looking needy. The result is a standoff where large numbers of people who would genuinely enjoy each other never once end up in a room together.
So the absence of invitations is not evidence about your likability. It is evidence about the era. Roughly one in eight American adults now reports having no close friends at all, up fourfold since 1990, and that number is not made up of uniquely unpleasant people. It is made up of people who lost the structures that used to put them in front of the same faces every day.
The second thing worth knowing is that liking is rarely the bottleneck. People who like you frequently do not act like it in any way you can detect. They do not text, they do not invite, they do not follow up, and if you asked them directly they would say they think you are great and had assumed you were busy. Warmth is felt privately far more often than it is expressed. You are drawing conclusions from a signal that most people never send.
Where the feeling gets its power
There is a loop underneath this, and naming it takes most of the force out of it.
If you believe people do not like you, you behave differently in a way you cannot feel from the inside. You hold back. You keep things light so you cannot be rejected for anything real. You leave early. You do not follow up, because following up when you are unwanted would be humiliating. All of that reads to other people as reserve, or disinterest, or being hard to get to know, and so they also hold back. Then you note that nobody pursued you, which confirms the belief.
That is not a character flaw. It is a perfectly sensible defensive strategy that happens to manufacture the evidence it is defending against. The way out is not to feel more confident first. It is to do one thing that the belief says is pointless, and watch what actually happens.
This is also worth separating from the related but different experience of feeling invisible, where the problem is not being noticed at all. Being unnoticed and being disliked feel similar from the inside and have almost nothing to do with each other.
The honest part
There are cases where something you are doing is genuinely in the way, and pretending otherwise would be useless to you.
The patterns that actually cost people relationships are pretty specific: cancelling repeatedly, only surfacing when you need something, turning every exchange into a monologue about yourself, never asking a question back, or being reliably heavy to be around without ever lifting. If two or three friendships have ended in the same way, that repetition is information, and it is fixable information.
Notice how ordinary that list is. None of those are "unlikable." They are habits, and the reason to look at them honestly is that habits are much easier to change than a personality, which is what you have probably been trying to fix instead.
If the barrier is dread rather than logistics, if the thought of a specific invitation produces real fear rather than reluctance, that is social anxiety and it responds well to treatment. It deserves better than being white-knuckled alone.
What to do this week
Stop trying to become more likable. That project has no finish line and it is aimed at the wrong target.
Do the thing the belief says will not work: pick one person who has been consistently pleasant to you and send one specific invitation with a day and a place attached. Expect it to feel unreasonable. Notice that a yes and a rescheduled maybe are both answers that contradict the theory.
Then get yourself into one place that repeats, and go back to it more times than feels natural. Being liked is downstream of being known, and being known is downstream of being seen over and over by the same people. Six visits is roughly where a stranger becomes a familiar face, and most people quit at two because nobody said hello yet.
And when someone is warm to you, take it at face value instead of auditing it. If a belief has been costing you years, the correct response to weak evidence against it is to believe the evidence.