It is well researched that helping others or just showing kindness to others boosts our own happiness, well-being and even health. Here is one article on the topic but you can google many more: https://thriveglobal.com/stories/why-science-says-helping-others-makes-us-happier/

It doesn't need to be a whole day's volunteering, or even something that involves a big self-sacrifice. A simple text message or email to a friend (or phone call!) to say you miss them, or appreciate them, or tell them why you're glad to have them in your life is enough to boost your own mood and trigger the momentum of having done something positive in your day. 

So even if you're feeling like you've got nothing left to give, and that you're the one that needs support and love, sometimes the best thing you can do for yourself is send out some love to others. It will come back to you with interest.