I've definitely been in this situation before and it can really begin to feel like manipulation. Really. It's tough AND it can be very emotionally draining - especially when, in most other situations you really really like this person.

What I found that worked for me (and this person is still a good good friend) is to be totally honest with them at all times. If you don't think something looks good on them, tell them.

OR what totally worked for me was to simply say "You know what really makes you look beautiful? Confidence!"

Now, that statement, I realized, could have gone either way. She easily could have heard something totally the opposite of what I meant, and yes, I had to hear the "you just don't want to hear this from me anymore!" (true, but guilt inducing nonetheless...)

Eventually it worked however. As did the "you know, let's just fake it until we make it" approach.

All the suggestions I made for self-esteem work totally fell on deaf ears, in fact, they just fanned the flames for additional reassurance because she had no self-esteem.

She's happy now. In a good relationship, in a good job and has a lot of good friends and I'm really happy to say that I am still one of them.