Oh hon if you're not in therapy for yourself, you need to be. You need to find out why you value yourself so little. What do you get out of the dysfunction and how can you meet that need in a positive way? Being the person who goes to great lengths to make other people happy at her own expense does something for you or you wouldn't do it - does it make you feel virtuous? needed? justified? like a martyr? worthy of approval?
You have boundary issues in the sense that you seem to not have any regarding how far people can intrude in your life and violate you. Therapy can help with this (there are some good books too). You clearly have no self-esteem either. Please, if not for you then for you children's mental health, seek out therapy. They WILL sense your unhappiness and they WILL pick up on something not right between you and your husband. They need to see you two as equal partners modeling a truly loving relationship in which each person treasures and values the other, not one taking advantage while the other lies there like a doormat.
I have been in your shoes affair wise. I can assure you that once is a terrible decision that can be rectified if both partners are willing to go to hell and back. After that? He's OUTTA here. Where is your outrage? Where is your self-respect? Where is your justified anger? Why aren't you making him win your trust back in words and deeds and attitude each and every day? Do not just roll over and die because it's easier than rising up and fighting for your marriage. If you love him, and if you think your kids are better off with you and him together, you dig deep and FIGHT for this. Let it get ugly. Scream and yell and tell him every hateful thought you've been holding in. Let him see that this hurts, that you still feel and that you still care enough to not just turn a blind eye. Let him know that he has to choose you or her/them. Forever. You know what? It's exhausting and draining. It's very hard to let yourself feel - it's easier to just go numb, build walls, fill your life with a million other things that take your time and energy so that you don't deal with this today, or tomorrow, or next week. Before you know it, years have gone by and it seems tolerable. Don't be that woman. You get one life - don't spend it with someone who values you so little.
And I know you don't want to hear this, because you know it. THIS is not love. Men who love their spouses as much as themselves don't do this, repeatedly. Mistakes get made - this is not a mistake, it's a deliberate choice, day in and day out, action after action, to show you how much he devalues you and dis-respects you on some level.
Marriages can survive affairs, but not the way that you and your husband are handling things. Start with therapy for you - make some phone calls and set up and appointment today.