How do you know if someone deserves you?

It's very sad and hard to hear when someone tells you that you deserve better than the person you are with. Even though that person is kind, gentle, and very loving towards you. Do people just say that because they are jealous of what the two of you have together and they can see how happy you are together?
They can't stand that they aren't as happy as the two of you are together so they have to say something to make themselves feel better.
That's just not right. Being jealous is never right, especially when you make the person you are jealous of question themselves. They have to throw a wrench in and say something to make themselves feel better. And I can tell when someone was doing this in my last relationship.
My boyfriend and I were living together and certain people would come over unexpectedly and see us together laughing and playing and they would see the batch of chocolate chip cookies he had just baked for me and my beautiful yellow rose's he would have the florist send to me. It had to be jealousy because they were so unhappy in their own relationship and we're stuck with an arsehole.
I would never say that to anyone. I would just be happy that they found each other and that a couple really can laugh and have so much fun together just staying at home together.
What you say?
How do you know if someone deserves you?
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