Hi OP,
I have experience of what you are going through as I have been having an affair for 6 months and have been through more soul searching than I care to mention during this time.
Affairs are extremely destructive and painful for everyone involved and to do the right thing would be to stay away from OM in order to properly focus on what you want, why you 'need' the affair and what you want to do to sort things out in the future. BUT, with so many conflicting emotions going on, I know how hard it is to come to that point of clarity.
With my situation, I am keeping things extremely discreet with the OM - I can't finish with him although I've tried because I'm completely in love with him, but I also love my DH and my family. To me it's as though the two situations are separate from one another. Unfortunaly the OM doesn't stop me loving DH, and vice versa.
The thing is you are in the midst of some extremely complicated feelings and you need to work through them properly. Don't do anything in haste, keep things as normal as you can, keep calm, but make a decision between the men involved as soon as you are ready to reduce the damage and come out with the right outcome for you and everyone involved.
I know I won't leave my DH because things, like you, are good enough between us and we have two DCs. However, the void that would be created by ending it with OM is just to much to bear right now. I'm working on it though, and am making changes in my life that will help me move on from him, without me feeling as though I'm foresaking my happiness for the sake of the children. I have to get over it properly - not end up like some other MNers who, years later, are still pining for their OMs because they've broken of all contact, which has left the sitation 'high and dry'.
I don't feel guilt because I feel helpless at the moment - almost like I'm a victim of the situation rather than the perpetrator, but I AM very ashamed of myself and feel like I'm letting everyone down by not being strong enough or moral enough to have avoided getting into this. It's not a 'happy' situation to be in at all so I'm not 'having my cake and eating it' like some may think.
You must realise that you are probably in the first flush of love/lust and so you won't beable to make a rational decision about your future until these feelings calm down a bit and you are able to sort your head out better. This is what I'm gunning for now - for some time to pass, for my emotions to settle down, so that I can think clearly. I'm getting there, slowly but surely.
MN is not the best place to discuss family destructive behaviour as you will get a thrashing, but what I've learned is not to take on the berating from others that are comfortably sitting in their own happy marriages, who have never dealt with an affair, and who believe that they, themselves, are not capable of straying off the paths of monogamy. These are not the best advisors - you, by having experienced on both sides, are far better placed to form an opinion so trust in yourself.
Try to keep a sense of perspective. You probably feel despair at the moment, but this will pass evenutally. It's better to ride out this affair until you are ready to properly move on (if that's what you decide to do) in my opinion, than try and do the right thing prematurely, finish it and forever go on pining for what could have been; like some ill-fated romantic tradgegy.
Bottom line is don't make a life-changing decision right now as you won't be in the best frame of mind and may indeed break up a good family life for what may just be a passionate, but brief, romance. Wait for the clarity to come and you will know what to do for the best. Good luck. You are not alone.