Remind them how much you love them, even when you feel like you do not have to say the words. You do. They need to hear your compliments. They need reminders you have not fallen out of love with them. They need constant reassurance because they are convinced they are eventually going to lose you and have been counting down the seconds until that becomes the reality.
When they push you away, be careful with the way you react. If you blow up at them for how distant they are acting, then they are going to shut down. But if you push them to open up to you before they are ready, then they are going to feel uncomfortable around you. The best thing you can do is remain patient. You have to encourage them to spill their soul to you, you have to give them reasons to trust you with their secrets, but you cannot pry anything from them.
When you love someone who does not see their own worth, little things can become frustrating. Watching them spend hours fix themselves in front of a mirror and still not liking what they see. Listening to their complaints about how they are expecting to fail and can never do anything right. Seeing them burst into tears and knowing there is nothing you can do to fix things.
Do not get too annoyed with them when they refuse to leave the house because they are having a bad hair day or because the number on the scale is higher than they predicted or because they feel like no one wants them around anyway. Do not roll your eyes when they reveal their biggest fears to you because you feel like they are overreacting. Do not give them any reason to feel like they should not trust you, like they should keep their demons to themselves because you clearly do not understand what they are going through.
When you love someone who does not see their own worth, you cannot treat them as horribly as they treat themselves. Even though they will comment on how much they hate their nose or their stomach countless times, you should never agree with them. You should never join that little voice in the back of their heads telling them they are not good enough. You should never tear them down because they are already busy tearing themselves down.
You can try your hardest to make them feel loved by spoiling them with surprises and compliments, but you cannot blame yourself when their insecurities continue to haunt them. You cannot accuse them of being ungrateful or wonder whether you are being a bad partner since they are still insecure even though they have you around. It has nothing to do with you. They are fighting a battle inside of themselves.
When you love someone who does not see their own worth, you have to hope that one day they will grow to see themselves the way you see them. As someone who is beautiful, valuable, and worth knowing.