I think it all depends on the people's personalities and the way that they're altered once they're in relationships. Because that's different for everybody. In general, the less often they invite you to hang out with them, the more comfortable it should be. My best female friend has had a couple of boyfriends. Her old boyfriend was a guy that I liked personally, but she would always text me to come hang out with them. Always. And it was because she didn't actually have that much of a connection with the guy and needed me to prevent her from boredom. In contrast, her newer boyfriend is kind of a dumbass and I can't say I care for him that much. He's tolerable in person, but he's kind of a screw-up and he always makes really inflammatory and offensive facebook posts. That being said, something has managed to keep them together for a long time and they seem able to function on their own. I still keep in touch with her, but I've only hung out with them a few times and none have been awkward at all.
My previous signature was getting old. This is my new one.