Stock that I bought one year ago, are all losing in value, however I'm getting dividends from it. I intend to keep them for longer-term because I'm quite young.

If I am not in need of money, no harm holding since it is still paying dividend.. Although if I see a good opportunity I might sell to recover the loss if the opportunity offset my losses in the long run..

Hold, they might rebound again in the future when the market conditions get better

Usually as long as a company continue to pay dividend, it proof that it is still profitable or solid cash flow. For instance, I bought Singtel at S$3 many years ago,although until now it is still like over -20% but I did receive dividend and therefore I still holding on

You have a long life ahead, you can afford to hold it longer term so no worries about holding it. Unless the company fundamentals and directions change