I know some people may not like this comment, BUT............I think your feelings are valid.
I think EVERYONE gets in a rut now & again and they start to feel burnt out. Whether it be with our jobs, our relationships, our eating habits, etc. So, what your feeling is normal!
Why are you feeling badly about something that you've taken control over for the last 2 1/2 yrs. of your life & now all of a sudden you feel like you just can't do it anymore? Maybe it's not your eating lifestyle at all??
I know personally I get in "slumps" where I get tired of cooking the same ole' things, eating at the same places (this could be either dining out OR eating at a friends house).
So, maybe your having some upheaval in other areas of your life right now & this is a side effect? AND you need some new recipes to try out? Maybe cooking a different way for awhile? I've heard alot of people cooking once a week & freezing the portions for the rest of the week when they don't feel like cooking? Could this an option for you?
Or maybe splurging on yourself & buying a new vegan/vegetarian cookbook that you've been wanting for awhile? Or even not cooking at all, seriously. For one week, eat some cold cereal & fruit for breakfast, a hummus pita with veggies for lunch, and a REALLY big salad for dinner!! At this point some convenience foods might even be what you need. Maybe this would give you some new inspiration?
Do you have a weekly meal plan? Do you know what your cooking on each night & when you go shopping do you take a list to make sure you have everything you need on hand? If not, then this one tip in itself will help you considerably when trying to figure out what your going to cook & if you have all the ingredients.
This has taken a HUGE amount of stress off of me. Not having to figure out what I'm going to cook every night & whether or not I have everything on hand was really frustrating me!!
Don't give up on something that you believe in so strongly & have stayed with so long.
As far as feeling like your putting people out with the way you eat? Others here have made some really good suggestions. Make a dish you like & take, or even offer to make the dinner at your house & invite your friends over?
I completely know when I start feeling burned out with one area of my life, I usually need to take a step back and try & figure out what's going on that's making me feel this way. More times than not, I'm trying to fit too many things in & I'm bringing on the stress myself.
Take care of yourself first & the rest will work itself out!
Oh! Don't forget to be proud of how long you've been a vegetarian, 2 1/2 yrs. is AWESOME!!!
Michelle