Hmmm.. I'm glad you've got a Relate appointment this quickly. I really hope that the therapist you eventually get (might not be the one you see tonight) will focus on your H's individual vulnerability to infidelity primarily and will take a more holistic approach to it, than just pursuing the relational difficulties. I hope you've come away from the script with which you began this thread, because that is so important. I so hope you aren't still buying this nonsense about neglect and lack of attention and can see that your marriage was no different to loads of others with very young children. After all, I'm sure you didn't feel adored and that your every need was being met, but you reasoned that this was life right now and it would soon pass as the children's needs receded somewhat. You didn't have an affair, did you?
Something jumped out at me from your last post. You thought he was going to friends' birthday parties? Whose friends - his alone or your joint friends? Were you in the habit of going to friends' parties without him then? How much leisure time have you been getting, while he looked after the DCs? I know he lied about attending these parties, but this was obviously a permissable activity in your relationship and I wondered why and whether it was equitable?
I can imagine your "bit of fun" rage, but try to find out what this really means.
I will say up front that I wonder whether that is a lie they have settled on themselves, to tell you, in order to hide their ongoing affair. His actions on the run-up to this don't support this statement at all. A bit of fun doesn't usually cause someone to want out of their marriage, or tell his wife that he's no longer in love with her. I really think you need to hear more about what precipitated this unburdening he dropped in your lap a few days ago.
I have heard this "bit of fun" comment in two scenarios.
The first is when someone has always had a discourse that affairs and flings are permissible, as long as you don't get caught or fall in love. This is why people who are perfectly happy in their relationships are able to condone philandering or serial infidelity - it is regarded as a relatively harmless enterprise as long as "everyone knows the score". Er.....except the deceived partner, of course......
The other scenario is the type of affair where it is an escape mechanism - not necessarily from the marital relationship, but from life and its stresses. A form of self-medication and escapist fantasy. While the involved partner might care for the affair partner's feelings and doesn't want to cause her harm, his feelings for her never go beyond infatuation and the most powerful feelings are about the enterprise of an affair itself and the positive strokes and ego-boosts it is giving the man. Usually however, the man is pretending to have much deeper feelings for the OW than he has and he does this to keep the affair going.
I really think it would be helpful to focus on the facts here and see where what he is telling you doesn't fit.
This affair has been going on for 9 months, not 6.
He cares about her illness and has been supporting her through this.
He felt so strongly about her that he told you he was unhappy with you several times and only a few days ago, that he was no longer in love with you.
He cared about the OW's feelings so much that he went to a call-box yesterday, yet last night he told her that she was "just a bit of fun".
I can imagine your hatred of her right now, but hard as it is, have a think about this difficult question:
How do you really feel about him telling a woman he's had a 9 month relationship with and who has cancer, that she was "just a bit of fun"?
Most of all, does that fit with what you know about his treatment of women and his character?