I'm sorry that life is unfair. I think it's important to remember that no one has everything and everyone has their own baggage of pain and suffering, no matter how privileged or perfect they look.
Negative emotions only hold us back and drain our energy. Learning how to redirect emotions into constructive work can help groom us instead of controlling us.
Redirecting emotions in different hobbies (cooking, art, reading, gardening, sports etc) help us become our own masters. We can't be slaves to our feelings.
Becoming slaves to our emotions only inhibits us from achieving our goals. People around us are only a distraction. We all run our own races. We only compete with ourselves. If we stop and stare at everyone else and compare our race to theirs, we never move forward, and never moving forward equates to losing.

Learn to love yourself and your life and create your own true happiness then you will feel happy for others as well as appreciate your own life and then maybe one day you will have a happy relationship

By focusing on yourself, and not what others have. I know it's easier said than done. All my best.

First you’ve identified what your problem is. But you also need to realize that your attitude is toxic and any potential mates are not going to be attracted to a toxic attitude like that. You are blocking any stable future relationships that you could have.

Just remember that most relationships don't work out in the long run. What you're observing is superficial plus your own imagination.

Figure out what you hate about them, then give that to yourself, then you will find someone who will give it to you

Find a relationship, or like me stay bitter and avoid couples where ever you can.

Join them

Only you can control that, alas. Your envy doesn’t hurt them, and doesn’t help you. You might consider getting counseling for help coping with those feelings—and ideas about meeting potential partners.

Recognize your own strengths. Talents. Gifts. Value. Just love you. 🙂

Create more happiness, excitement etc in your own life partner or not