There's no one right answer to this - but there are two different issues: playing guitar, and writing songs. While they are obviously connected, they are independent skills.
You will get better
at guitar the more you play - simple as that. Doesn't matter what you play, as long as you are listening to what you do and modifying anything you do if necessary (ie if it doesn't sound good).
Learning other people's songs will tend to make you a better
songwriter. That is, it will teach you more about how to get the effects that other songwriters get.
And the more songwriters you study, the broader your compositional skills will get. (This would be how professionals go about it. It's like learning any trade: you study the masters and copy them.)
At the moment, you may not be aware of it, but everything you compose comes from something you've heard before. All the music you've heard in your life has gone into your brain somewhere. It's just been somewhat haphazard and piecemeal, unless you've sat down to consciously learn a song. So you're inspired by others whether you realise it (or want it) or not.
The only question is how conscious you want to make the process. If you feel your own songs are good enough now, that's fine. But if you feel you get into a rut at any point - that your songs are starting to all sound the same - that's a sign your inspiration is running dry. So you need to top it up. You will need to listen to a lot more music, and start absorbing some different ideas.
Again, you may not need to sit down and work anything out note by note. Often just hearing something can set you off down an interesting new path of experimentation.
Similar things apply to guitar paying. You can teach yourself perfectly well, just by trial and error - up to a point. It's only when (or if) there comes a time where you feel you're stagnating, or have reached a plateau, or hit a wall. That's where your self-tuition has run out of gas. The same advice applies: get out and look for some new stimulation - maybe some different kind of guitar playing. Or get lessons of course.
I don't think you need to worry about it right now - as long as you feel everything is OK right now. If you hit a rock some way down the line, well you can deal with that when you get there. It's possible to teach yourself bad habits, but as long as you stay inquisitive and keep trying new things, then you will improve.
It's actually interesting that you're worried about "getting better". That's a sign that you don't think you're very good at the moment. Fact is, probably everybody feels the same way! Nobody ever feels they're as good as they're ever going to get. The mistake is to always focus yourself on some future goal, some hoped-for level of skill that you're working towards. Never do that! Long-term goals are a BAD THING. (The only real long term thing is death...
) Short term goals are fine: something you can achieve today, or tomorrow. Otherwise the only worthwhile goal is to enjoy what you are doing NOW.
If you're always thinking about getting as good as some other player you've heard, you'll never be satisfied. There'll always be someone better than you. And there'll always be someone worse than you. I'm not saying you shouldn't want to improve - but you should only compare yourself with how you used to be.
"Improvement" as a musician is only about realising your own aural imagination as best as you can. You can do this from moment to moment - it's not a long term plan. However good you are technically, it should always keep pace with your imagination and understanding. It's quite common for one or the other to edge ahead occasionally - because progress is not a smooth gradient, but goes in fits and starts - but then you work on the other to help it catch up.
So you only need to decide on what aspect of your playing (or creative thinking) you are
currently dissatisfied with. If there is nothing - great! Carry on. It's silly to worry that by some point in the future you won't have "improved" from where you are now.