5 Answers

Yes and why?

It is possible...but unfair to all three especially the one you are currently with. She will feel cheated regardless of whether you were physically involved with the other woman or not. Get uncomfortable and be fair to all involved...staying "comfortable" is selfish and holding her back from finding someone who would love to have her in his life.Not to be rude but "piss or get off the pot".I hate the expression but it means what it means.If there are kids involved make sure this other woman is really love and not just out of boredom.Talk to a councellor or something to be sure this is what you really want...kids aren't as resilliant as they say.Your decisions can stick with them for years.

Just be honest with yoursel and your friends

yes! and you need to re-evaluate your life. what is more important to you? comfort or true love? Be fair and sincere to yourself and the two ladies. They both deserve to be loved,cherished,respected and appreciated,and so do you!
Who understands you the most? who can you 100% be yourself with without barriers? If you have kids with the "comfortable" lady,sort it out,kids are not dumb and they'd rather have 2 happy separated parents than 2 miserable parents living under the same roof. Staying JUST for the sake of the kids isn't a good enough answer. Follow your instinct.

All the best.....