This tantamount of "using" a pet to improve your life than genuinely care for them. What could happen is once you improve your life, you may slowly start detaching from it and throw out. That special bond may not form, if you only buy/adopt because you are depressed.
In that case, you're not using an animal to improve your life. At most, you're forcing yourself to look a bit outwards and focus your energy on an animal, in other ways put strain on yourself.
Most pets love you unconditionally back, as long as you don't abuse & neglect them knowingly. They will look after you and motivate you to continue having this feeling by looking after yourself, too.
Losing a loved pet can leave a scar which can last a life time. I still miss my pet bird, which lived for more than a decade, and died peacefully, and brought limitless joy to everyone in the family, by loving, demanding attention and trolling us.
Animals may look simpler than us, but almost all of them know the language of love and care way better than us.
