I do loan out my makeup and give away things I don't get the use out of.... I am a woman who buys way too much makeup, and I tend to tire of things quite easily and move on to something else.
At the same time, I do love pretty much every item I've ever bought and keep stuff I don't use much because I am stupidly and weirdly sentimental about makeup, esp MAC. I love to open up my makeup box and dig right to the bottom, pull out something that I ain't used in a while, play around with it and see what I can come up with - a new combo or something. It's all the fun of having a toybox when you were a kid, but for grown-ups
and a great creative outlet that I treasure and jealously guard.....So I'm weirdly possessive about my makeup even though I *do* frequently loan items out.
My willingness to give stuff away/loan it out tends to be proportional to how much I spent on it, how easy it would be to replace, how much I like the item, how much I like the friend and also how good it looks on him/her!
I ended up eventually giving one of my favourite non-MAC lipsticks to my boyfriend EVEN THOUGH it was dc and a present from another friend because he really fell in love with the colour and kept borrowing it... but I was a bit sore about that, I didn't like to part with it at all, because of it being d/c and a gift, the only reason he got it in the end was he'd used up so much of it when he borrowed it that it seemed ridiculous to keep asking him for it back....
However, when I bought my first MAC blush and found it really didn't work for me at all, I was delighted for him to have it, because such a beautiful and comparatively expensive item needs lovin' that I wasn't going to give it.
I also gave a not-particularly-expensive but bloody-hard-to-find and beautiful e/s to a friend who was feeling very low and unglamourous due to some hard stuff going on in her life. I tried a bit on her and it looked AMAZING, and it was the first time I'd seen her smile in a while, so I said "look, you should just take that, the colour's GREAT on you babe I insist".
So I guess I'm a great big softy and although I'm really, really, really emotional and sentimental about my makeup collection (very few of my friends understand why I get so excited about mu), I'm *more* sentimental and emotional about my friends, so I do end up loaning stuff out or giving it away to people I care about.
And yes, sometimes I do regret it, lol! One of the most irritating things in the world is to find that a friend has lost or thrown out something I've given them - I tell myself "it's only makeup" but it feels like TREACHERY, lol!