I have some friends I see about once every 1 1/2 - 2 months and when we do it's lovely.
However, one by one they are now all bringing their partners. The first friend it was like ' fine, ok', but now as I am the only single person, I feel I will be like a sore thumb.
To be honest I've been dating but single since my last LTR a few years ago and usually I'm not bothered but I actually feel a bit upset about it lately and felt crap during valentine's.
At the same time, they've invited their partners now and will look petty to say anything. Wwyd, go along this time and say something if it becomes a habit? Or bring it up now and sound like a grump? 
In a way I feel like bowing out and letting them all be together with their partners, but then I'll just be alone for the night!