What happens if you have bipolar? You carry on with your life, same as you do now. You take medications to help stabilise your mood. You look at things like CBT and other therapies that can help you manage your condition and you carry on living, but with more understanding of the condition.
But I'd not get ahead of yourself yet. It takes 13 years to become a consultant psychiatrist and even they can't diagnose by looking at symptoms as explained on line or by simple observation like your friends.
Mood swings can be down to so many things. Hormones, cyclothymia, personality disorder, bipolar, thyroid problems. If you're frequently depressed, the difference between your depressed self and your happy normal self can look like mood swings too.
If you think you can manage the way things are and anti-depressants have worked for you before, keep taking them and ask about talking therapies to help you work through the depression.
If you want to work through possible alternative causes of your moods, then speak to your GP about your concerns and ask if it would be possible to get a referral to a psychiatrist for a proper evaluation. They can do a proper diagnostic interview where they can explore all of the possible causes of your mood swings.
FWIW, I have bipolar and it's not scary, it just is what it is. I take meds for it, I've had therapy and I carry on living my life as normal.