But based on my findings:
They are open with you about what's on their mind and going on in their life and honest about how they feel about you and your relationship with them, they dont lie or play pretend about their emotions towards you
They are very open to communication with you about anything on your mind and willing to talk things out with you when possible
They don't get mad at you and argue with you all day everyday over little things or at least don't let those things come between you and them
They value spending time with you and are usually happy to do things with you
They ask questions about you and how you are
They want a future with you in it
They aren't demanding or controlling over you
They love being able to text you or talk with you first thing in the morning and just before they fall asleep and throughout the day when they can
They usually try not to forget when your birthday is or any special day you two have together
They enjoy planning things out with you that are just for you and them
Sometimes this may not always mean a truly happy relationship but they have introduced you to their family
Probably the most obvious, They tell you they are really happy with you and value the time you both share together and wouldn't do anything that would hurt you.