I urge you to deal with each day one at a time. No one can realistically meet a goal like, "I will be happy in six months". You should focus on being happy now...today...at this very minute. This is why you like the gym. It makes you feel good while you're doing it.
In your black mood, you may not quite be getting it. Happiness is simply there for you. It's the way you were meant to be. It's your biological birthright, as it is for everyone.
People who are depressed think they see the world as it really is. They notice that the lions are eating the gazelles. That may be true, but what they are failing to do is to think positively, as we were also designed to do. We were designed to be eaten by lions, but we were also designed to be happy regardless. Unhappiness is actually dysfunctional, a denial of the natural happy state that evolution designed you to be in.
Imagine a gazelle living in anxiety and regret. It regrets the many other gazelles who were killed by the lions. It has intense anxiety about what might happen. A painful and horrific death (being eaten alive) can come unexpectedly. And yet this is not the way it is: nature has protected these gazelles and freed them from regret and anxiety.
We have higher cognitive functions than a gazelle. We experience regret and anxiety, whereas they experience just fear. But the same principles apply. We should be living without regret and without anxiety, contented and enjoying life. Like all animals, this is what we were designed to do.
There are many different cures, including pharmaceutical and other things. That's why you should marshall your resources and find support IRL.
One cure is to take advantage of the relationship between cognition and emotion. Your emotions are based on what you are thinking and telling yourself.
Think about terrible news (eg the death of someone you love). Before you hear the news, you don't feel grief at all. It's only when you are told the news that the grief starts. It's not the death itself that is upsetting but the knowledge of the death. It's not the external event or situation, but what you are thinking about it. First cognition, then emotion.
This principle applies to everything you think and feel. If you think positive things about events and the world, your emotions will follow suit. The emotional upheaval is rooted in what you're thinking.
Imagine a man who has been in a terrible relationship for 10 years. His partner was an alcoholic, let's say. After he finally breaks up, he is intensely delighted to be free of this burden. He is really happy being single. And yet another man has not been in such a bad relationship. He feels very unhappy being single and alone. Both men are single and alone, but they are telling themselves different things about being single. The emotions they feel follow what the different things they are thinking about the very same fact.
This is why therapists try to get you to talk about things. They try to get you to think about things realistically so that your emotions will follow suit. However, you don't need therapists to do this. You can simply train yourself to see things positively, even the bad things. One way to do it is to constantly tell yourself, "is this negative thinking helping me?"
Another truth is that getting what you want (eg love) may not have the positive result you hope. It may not affect your mood. You may be just as unhappy because you have not addressed why you feel unhappy about things. Happiness is generated from within, by what you're telling yourself, not by external events, not by love. Many, many people who are not in love are perfectly happy.
Yes, I'm afraid it's that simple. It's like a light switch. You make a commitment to yourself to stay happy no matter what. And then you guard that commitment by monitoring your thinking and cutting off the thoughts that threaten your serenity. A few short minutes. "What am I thinking about this?" "Why is it bothering me so much?" "Is this helping me?" "Is it in my best interest to think this?" "Can I let it go?" "Can I see it positively?"