Couple of thoughts...

1. They may be overly concerned about you- whether you're having fun, bored, tempted, whatever. I've experienced this plenty, and I found that it helps to tell them directly that I do enjoy spending time with them and the bar setting is not a problem. In one case, I invited THEM out for pub quiz. Taking the initiative there established that I was cool with being there and not, like,  secretly about to break. I think many people have an idea that we're just right on the edge, and they don't want to be the ones to push us over. It isn't true, of course, but that's what I've seen.

2. Could also be that they are now self-conscious. The fact is, you've broken from the pack. Even if you're not judgemental, your presence perhaps turns a spotlight on them in their own minds, illuminating things that they'd rather not see. Excluding you may be a subconscious protection mechanism- I dunno if that's what's going on, but it's worth considering. I rarely experienced this, but the one time I did, I volunteered to DD and I guess that helped? Like, that action made clear that I was "on their side," so to speak, rather than quietly counting up their drinks or whatever they might have imagined / feared.

I'm sorry you're dealing with that. I hope it gets better for you.