First, I just want to respond to some of the 'covert' comments made about 'choosing' to have children out of wedlock. It is truly a shame to me that someone would post a legitimate issue about what to do in an intimate relationship in distress, with the same intentions all of us have when we post a question....the intention of soliciting meaningful and supportive advice or insights....and that people would choose to insert some sort of weird judgment about something that has nothing to do with the question posed. Marriage is not the issue here, a relationship in distress is and I'm so happy many of the posts responded with kind hearts.
That being said (and sorry to hijack the post momentarily Leonor!)...to focus on your partner for a moment, is she on any pain medication for her back injury? If so, how long? Two things: Pain in and of itself can be very depressing if it's chronic, and pain medication can actually contribute to and intensify depressive symptoms.
Is your partner aware of her depressive symptoms? Sometimes gaining awareness is a pretty valuable tool in resiliency. Couples counseling might provide her an opportunity to share her stresses and depression with you in an environment that is relatively safe to speak in and an environmentally safe for you to express things that are also safe. And by safe, I mean any triggers that occur are somewhat contained and worked through in ways that don't afford either of you the opportunity to fall into less than constructive reflexive responses.
Depression is a very tough thing to experience and if you add pain on top of that....I feel for your partner.
Now about you...it is REALLY tough being around depressive energy all the time, especially with a life partner. The tough part is walking on egg shells...is today a good day? Is this hour going to be rough? What does her expression mean? Will there be a quiet and negative energy and for how long? And these are just a few questions you might hear yourself ask everyday. I feel for you.
Counseling might help, but what also helps is to NOT GET LOST in someone else's suffering. You can love them and care and want better for their life experience, but you cannot control another persons mental well-being. What you can do is control your response to it and to what extent it influences your other relationships, including the one with yourself and your kids.
Only you know if it's time to throw in the towel. And no one here can advise you on that. When you are done, you are done and you know. If you don't know, then you aren't done. Just make sure if you stay or leave, it's for the right reasons and not out of guilt or obligation because your kids will pick up on that.
I say, prioritize repairing what you can in this relationship, regardless of if you stay or leave, because your kids have two parents and always will. How you treat one another will influence how they treat others and how they treat themselves.
SO my two cents...okay, more like 47 cents:)...try to resist the urge to get caught up in specifics and focus on the big picture...well, 5 big pictures. One for you, one for your partner, one for each chiild, and one for the collective family unit that will always be regardless of staying together or breaking up. Once you do this, who invited the mother and sister is irrelevant because it's a problem impacting one or more of the big pictures. I hope that makes sense!
I wish you well on your journey...I wish your partner well on her journey...and I wish your family well on the collective journey. I didn't read anything that indicated anyone is the bad person to blame for everything and think you actually respect your partner. Something that a marriage certificate cannot possibly dictate.
Best wishes and focus your love on your kids when things get tough, because sometimes kids have a way of pointing our the obvious even when it isn't so obvious to us:)