When you're with him/her, you feel secure and know that he/she has your back. You don't have to worry about being betrayed or disrespected. You know that he/she only wants the best for you. Sometimes your gut feeling can tell you if something's wrong with a person too (but of course don't rely on it).
2. You feel happier
There's no point of being in a relationship if you're no more happier than not being in one. Happiness is a good indicator of how much satisfaction you're getting from the relationship. It is certainly not the only one, though.
3. You feel balanced
You feel that you're at a point where you can invest in the relationship while having your own space. It's not healthy if a couple always has to be with one another, that'll be close to experiencing addiction. A good relationship requires an appropriate proportion of having space and spending time together.
4. You feel you can confide in him/her
A good relationship should have minimal barrier. He/she will probably be your best friend and know you like no other person. You can confide in him/her without feeling like you're being judged. Over time, you'll only grow closer and know each other better.
5. You feel comfort that's like no other
When you're with him/her, you feel a sense of comfort that you can't find in anyone else. Time passes quickly when you're with him/her and you absolutely enjoy being with him/her. You have fun without feeling the pressure to be someone else. Love doesn't always have to be passionate; it can be calming and peacefully joyful.
6. You don't ever want to lose him/her
You find that person so valuable and irreplaceable that you don't ever want to lose him/her. You want to spend your life with him/her, it's difficult to imagine life with anyone else. He/she holds a very special place in your heart.
7. You feel you can better utilize your potential
A good relationship can help you see and use your potential. You can discover different sides of you and be able to explore some aspects of you that you never knew were there. Maybe you've come to realize that you can actually be a funny person and make people laugh in your own way; maybe you discover that your cooking is considered good in people's eyes. A good relationship can help you open up and grow.