NC, as this is incredibly outing to those who know me... 
I have 3 children with my STBXH. When I was ill 4.5 years ago (a coma and died a few times) he cheated on me by talking to other women sexually, whilst I was in the house, sending them pictures etc. and ultimately arranging to meet someone for sex whilst he was on a course in London, staying in one of my parents properties (I was 3/4 months out of hospital and, whilst still not up to looking after three children alone, knew his work was important to him). She didn't turn up, but messaged me to let me know of his actions. He admitted it and a long story short, I tried to forgive and move on. A year later I found that he'd done the same (although to my knowledge at the time he hadn't tried to meet anyone in person) and when I confronted him he decided to leave me and the children because "he couldn't hurt me anymore". He blamed his mental health, which he said was caused by my illness. (Septic pneumonia caused by a womb infection when I had my youngest child 11 weeks prematurely.)
After he left me, and I was very vulnerable, he told me he wanted to come back eventually, and in my vulnerable state I believed him and we slept together semi regularly. (All whilst he was taking the piss with childcare and would have the kids 3-4 nights a month....it's not much better now). He also refused to tell my family, who still are very supportive of him given the bond they made when I was ill, what happened, and as a result a couple of family members think I caused the breakdown of our marriage. I eventually saw the light, saw he had no intention of trying to reconcile and have moved on. I have a lovely partner who I love and trust, and is a wonderful step father.
Until last year my STBXH was living with one of my family members (as he couldn't afford elsewhere until I bought him out of the house). He moved out and one of my family member's friends, who is my age, and has become family, moved in. STBXH has been messaging her quite a lot (very unlike him unless he's interested) and "apparently" thinks he wants more. She has no interest.
I don't know why...I can only assume it's from previous actions making me feel like a fool...but the idea that he was trying to "get with" my family friend, has made me feel sick.
I genuinely am happy, and want him to be too, but not with a practical family member.......
Can someone talk some sense into me please.... 