Hi Catsim! 
I can only answer your questions from the perspective gleaned from my own experience shared here in the hope that it proves useful to you. Here's how I see it. Starting with the most essential.
Ultimately motivation to persist beyond the novelty of anything new and titllating must come from within once the initial excitment of its novelty has worn off. From experience, look to what your real motivation is for wanting to play guitar. Learning takes time and perseverance. It's an endurance event, not a sprint, and not as easy as the likes of guitar manufacturers' spiel would suggest to foster sales, or everyone would do it.
Playing alone ...is what I would suggest the overwhelming majority of guitarists do do, especially amateurs. If the playing part regardless isn't what appeals, then ask yourself what it is that does. There's your answer because 90% of anyone's playing will be practising alone most of the time.
As to your other questions.
My motivation. The challenge in learning something I always had a desire to complete which is complex requiring the acquisition of skills which in turn requires self-motivation, determination, persistence abetted by the fact that I am truly enjoying that journey.
Recording and uploading. Recording yes, for self-analysis. Uploading. No. Why would I want to? I have no pretension to You Tube stardom, nor desire for accolade or recognition from an audience other than my critical self.
Play and pick own songs. To the first part no. YMMV. My current objectives are A. to play 'reasonably well' (how long is a 'piece' of string?) within 4 years, and B. be able to learn and play most of the the songs I love to a high standard of demonstrated competence by the end of that time frame. Original compositions aren't even in my radar whether as a means of expression, seeking recognition, or fame & riches - it's well past that 'midnight' for me. By "pick own songs" not quite sure what you mean by that?
As for the encumbrance of time managment of a flexible schedule and travel, I think that's one of the most fantastic things about a structured online course like Guitar Tricks offer. You can organise your lessons around your schedule to fit into your life, from anywhere, and it's so affordable and effective. If only I'd had something like this available to me 45 years ago!
"I'm not sure if it is still interesting to learn guitar with an online course after 3 months?" Is that a serious question? Unsurprisingly, three months in I still wasn't playing quite like Page, Slash or Clapton, was far from bored, and 9 months in there's so much here for me to learn and find interest in, I surmise I'll be renewing my annual sub whenever it rolls over for some years to come. Again, the usual net disclaimer YMMV.
For playing of an evening not disturbing others. Buy a cheap electric guitar and use a Vox AmPlug or similar headphone amp. Or a travel guitar with that capability if that's in your budget. It'd be prioritised in mine if I really wanted to learn to play in your circumstances.
Lastly, the tough one. " ..maybe some of you can help me with my motivation?"
One can offer guidance and anecdotal encouragement, but boosting someone else's motivation with a pep talk only lasts short term. Ultimately the passion, desire and drive must come from within. Only you can know the sincere answer to that question.
