I’m assuming you are single- and I would go with apushatayid’s suggestion of wearing a ring. Except that you don’t have to actually wear a ring (although it does help).
But you could just send out the vibe/message that you are married/ taken. (I try to think about how I feel when I’m dating someone seriously and a different guy gets suggested/ tries to talk to me) It makes a person want take a certain step back on an emotional level while still being open and nice.
You need to imagine and act as if you are married- so they get the message that you are ‘taken/not available’ but are just being friendly.
I used to make references to the guy I was dating (pretending that it was a long term thing so that they would see it as serious and leave me alone). But if you’re just starting out and they don’t know you yet… pretend you are married- it really makes things easier.
Do not feel that you have to go for lunch or whatever with the group if you are not comfortable with that (go with the women if you are comfortable with that- you don’t want to come across as a total loner)
It’s hard to learn how to balance this- but it’s a very valuable lesson to learn, and well worth the slight discomfort in the beginning.
Good luck!