"...later on down the line and she leaves the guy she is with and wants to to come back and work on the relationship and get the fam back together; should i consider it?"
In 2 words, HELL NO!
I have been lurking on this site for the last couple of weeks and was COMPELLED to register today just so I could answer you. This woman is USING you. You are her fall-back position. You are her ace-in-the-hole. You are her 'better than nothing' guy.
This woman does not love you. It is obvious to us (and do not doubt that it is obvious to HER) that you love her. She is using that against you.
She cheated on you with OM.
She cheated on OM with you (and God knows who else).
She is trying to stay in your good graces by dangling 'maybe in the future' in front of you so you'll stay interested. When she says 'when she figures herself out she'll want the family back' she is lying (or deluded). She wants to eat her cake and have it too. Not possible.
Do not believe for one minute that she will leave this man for you. If that were the case, she would have done it already at some point in the last year. I think she likes the house and the freedom to come and go that he gives her (since she obviously has freedom to come over and boink you! By the way, the boinking was called off by YOU, not by her. She obviously has NO moral concerns with being faithful to anyone.)
Have NO DOUBTS that if she comes back to you in the future and wants to 'work on the relationship and get the family back together' that what she really wants is someplace to live because he either (a) kicked her sorry, cheating ass out of his house when he found out what a skeezy snake she is, or (b) he has gotten tired of her and has moved on with some other woman and left her high-and-dry and homeless. I do NOT say this because you are un-lovable. Not at all true. I say this because she is a screwed-up USER who is only concerned with her own short-term happiness.
In the future, do NOT let her into your home again. Not even 'temporarily' while she gets on her feet. Not even for one night. Not even if it is pouring rain with lightning striking all around her and she is soaking wet and looking all pathetic. If she shows up wanting to 'reconcile' you can bet she just needs shelter, food, and utilities paid. Offer to take the kids in since she's homeless. Offer THEM love and shelter until she is back on her feet. But do NOT offer love or shelter to her; otherwise you'll be back on this forum in 6 weeks/6months/6years (however long it takes for her to start cheating on you AGAIN) with the same story and a re-broken heart.
You need to focus on YOU. Why do you want to be with a woman who doesn't want to be with you, disrespects you, is untruthful, unfaithful, and incapable of being in a mature loving relationship? Don't YOU deserve better? I think so! And so does everyone else on this forum! You need to fix YOU. You cannot fix her; no-one can except her.
You need to focus on your children. Is this something they need to see? Their father is being played for a fool (but only if you allow it), their mother is acting like a selfish, immature tramp. Of course the children are suffering. The only way you can improve THEIR lives is to improve YOUR life and show them a better way of living, an honest way of living, a mature way of living.
You need to let go of her COMPLETELY. If you can afford counselling, get some. Even people with limited resources have options available through the government or religious institutions. I would not recommend that you get into another relationship until you work on your self-esteem issues for at least 6 months lest you fall into another unhealthy relationship because you haven't acknowledged what led you into this current one.
Good luck to you, Sir F. You have a long, hard path to travel, but in the end you WILL be a better man, a better father, and, hopefully sometime in the future, a better husband to a WOMAN (not a selfish woman-child) who appreciates the efforts you have made to live a strong healthy life for yourself and your children. In 2 years, you can make GREAT STRIDES for yourself and your children (and hopefully you will) whereas your ex will still be bouncing on her back from mattress to mattress wondering why her life doesn't work!