Don't be sorry for telling people how you feel, it's perfectly human to feel how you do, because if you're losing weight and other people around you are slimmer, then it's obviously going to affect you to some extent even if it's just now and then as opposed to seriously wrecking your confidence.
The thing is it's about what you do not them. They may look slim, but what's the picture inside?
Slim people can still be at risk of things like blood pressure and cholesterol issues and Bone issues, if they don't eat enough, or don't have foods that contribute to cholesterol reductions or are high in salt perhaps coupled with a frequent caffeien intake, as caffeine can contribute to constricted bloodvessels and Salt can increase Hypertension risk and not all Salty food is automatically laden with fat as well.
Even active healthy people can be at risk of Cholesterol issues, if it's a genetic thing and may find that things like whole-grains or an increased fatty acid intake may be beneficial in curbing the problerms faced by a body that is a little more active in cholesterol production than many other peoples bodies.
Plus those people may have slightly unhealthy bone density if they don't eat enough of the right things.
So those people are not necessarily as healthy on the inside as they may look on the outside. Your main focus must be you, not them, and if you want to tell people who you feel, you're perfectly entitled to, because you just might speak to one or more people that feel similar to you, but think nobody would understand them properly.
Keep on telling people how you feel, as it all helps the rest of us to do what we feel is best for you
Overall your efforts have bene pertty darn great, so be proud of yourself, because you deserve to be