I currently have the UK student visitor visa, valid until 26th of February. I am done with my semester in the UK, my studies are officially over but I really want to visit my friend in England for couple days in February. Is there a chance that I will be refused to enter the UK, because I am no longer studying there? Please note that I have been refused the UK visa in past once, but was successful the second time.
No one can accurately predict what will happen during your landing interview, even with a lot of personal details about you anyone taking a guess would be doing just that: a guess.
You're a bigger flight risk because you have no reason to be in the UK and seeking to enter the UK on a student visa where the course is finished gives them the right (but not the obligation) to remove you under Paragraph 320 of the rules.
(1) the fact that entry is being sought for a purpose not covered by these Rules;
They don't have to use that paragraph if they think it isn't necessary.
In comments you wrote that you plan to tell them you are visiting your bf. That provides a legitimate premise for your visit and improves your chances of getting in. IO's know that students can form romantic relationships during their time in the UK and you wouldn't be their first case; they like it much better when somebody does not try to play cat and mouse about it. It becomes problematic for an IO if they think you will overstay and try to use Article 8 to settle here. If the IO gets that idea, you will be removed (or given temporary admission).
As always, landing interviews are governed by personal impact and articulation skills. Having a legitimate premise is a bonus. Presumably you will stay with your bf, so your accommodation and maintenance are sorted.
Make sure your bf is in the arrivals area and reachable by mobile and/or SMS. They have the option to interview him separately.
Returning to your question...
Is there a chance that I will be refused to enter the UK, because I am no longer studying there?
Yes, this is a nascent possibility. Nobody can predict what will happen. Having a romantic interest in the UK does not, in itself, indicate an intent to break our laws, but if the IO's radar is alerted anything can happen.
Per standard advice: if you want a smooth transit through UK immigration controls, get an entry clearance and remove all doubt.
NOTE: the same option that you used last time is open, i.e., come to the chat room and talk about it.