Having an affair with my separated husband-complicated. Married 14 yrs, together 18 and 3 kids?

Husband & I separated 8 months ago b/c of bad financial strains & communication issues. 2 months after, he began seeing someone. A month after that, we started seeing each other again, no but dating, talking about our problems, figuring out what went wrong & if we can have a future together. It's now month 8 and we have continued dating-no but kissing, flirting,etc. He is "cheating" on his girlfriend with his wife. We went out last week-had a great time. Had serious discussions about what it will take for him to come back home. This week he accuses me of sending his girlfriend nasty evil text messages which I did not. My phone records show I did not. He said he saw the text messages & my phone# was on them. He's upset-feels I've ruined all the progress we were making while he's trying to sort out his feelings. I'm upset b/c he's like Jekyll & Hyde & won't listen to me, look at my phone records, etc..Cold feet I guess?I guess I should forget him & move on but it's hard?