I would first ask myself "Do I want to go to the parties?" and if the answer was 'yes'
then next time they ask say "I might like to come again, when is the next one?"
If they say 'oh, next saturday' ask if you need to call anyone to let them know you are coming (always a nice thing to do) If they say 'yes, maybe you should' then call them and say '__ and _____ said there was a party on Saturday, and suggested I come, may I invite myself?' and they say "yes! " and then you say 'thanks!'. . . or they say "'erm. . ah. . .oh. . .aummm" and you say "oh, well, maybe another time, see ya' and you're done.
easy peesey. . stick to the script
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Alis volat propriis
State Motto of Oregon