i know what you mean. i'm very heat intolerant.
1/2 to 1 degree in body temp can cause a pseudo flare/symptoms (sx's) of MS.
your friends need a bit of education. maybe you could print off an article or 2 about heat and MS. if they're really your friends they will understand.

there are cooling collars that you can find in Walmart for about $5.00. they help to a point. there are cooling vest that various companies sell for about $100 to $200. you could also check out MSAA website. i think they help out also.

the vests really can work but are limited to 4-6 hrs depending on how hot it is outside.

when summer really hits i have to plan my days differently. like grocery shopping early in the am. i just can't do much outside. i get severe muscle weakness, short of breath and very tired.

i hope you can find some relief.