I'm in a long-term dysfunctional relationship with the father of my two children. We're not married (my choice for reasons below)
Two years ago he was unfaithful to me whilst I was heavily pregnant, his actions caused me significant emotional harm and I believe was the tipping point for me developing PND which took a long time and therapy to get under control.
The OW became pregnant so he now has another child very similar in age to our youngest. I have never had any ill feeling toward the baby itself but having to accept the OW is now tied to DP forever has been very hard.
I took him back before OW baby was born and agreed to try again, I had firm boundaries and conditions but in hindsight it was a load of bollocks. At the time I thought it was best for our children, but to be transparent a large part of this was because i didn't want to be a single parent. My mental health was shot to shit after what he'd done and I didn't think I would cope alone.
We have rumbled along ok for the most part since but I've never fully gotten past what he did, he hasn't gone above and beyond to make me feel secure in the relationship.
There is no sex life, no intimacy and I'm afraid I just don't love him in the same way anymore. Emotionally I have checked out but we remain together and under the same roof for a variety of reasons, the main ones being finances and convenience.
Fast forward to now.
I've been invited for dinner and drinks by somebody who I am in my own admission attracted to, the feeling is mutual. They are single. I'm not looking to have a relationship with this person but I would very much like to go along and enjoy myself, have a fling if you will. I've been depressed for a long time and had nothing to look forward to, but since this person came on the scene I've felt a little spark come back. I've felt noticed and beautiful.
I haven't sought the opportunity out to extract revenge, and have found myself feeling extremely guilty at the prospect of going along - if he happened to kiss me, I already know I wouldn't pull away.
I've been fiercely loyal to DP for many years and wouldn't have dreamed of doing anything like this before now, even in the early days after finding out about OW I wouldn't have cheated in retaliation, but as time as passed and I've fallen out of love with him I'm now thinking "Well why shouldn't I?"
I feel guilty even saying it. This isn't me, well it wasn't anyway 
Can I have some advice please, would you go along or not? Feel free to annihilate me and bring me to my senses, I'll probably be grateful later on.