If you weren't divorced yet, he had no business getting involved. MANY couples separate and get back together or go through divorce proceedings only to have regrets...much like it sounds you did yourself.
Until there is a CLEAN and PERMANENT break between a couple no one else should get involved, and to be honest, he should have given you at LEAST three to six months before suggesting the two of you get involved. He gave you NO TIME to grieve your marriage or make any sort of transition..he rushed you, and you were vulnerable and allowed him to rush it.
Sorry, but when one person is hurting, lonely, emotionaly confused, and hurt from a relationship in trouble...and some other person comes along and offers a new beginning...i DONT feel at ALL sorry for that new person if the hurt person goes back to work on their marriage.
NO ONE should be getting involved with someone who doens't have a clear head and heart...you ARENT helping. A lot of people seem to think that offering someone a new reltionship with them is good therapy for hurting over the loss of another, it isn't. People need TIME to HEAL. He gave you NONE.
I understnad you likley lead things on as well, but when someone is hurting, you don't HIT ON THEM or offer to DATE them...you be a FRIEND, or if you CANT keep uninvolved then send the hurt person to someone who CAN control themselves.
HE had a clear head, you were hurt from your marriage ending. He never should have gotten involved...and he knows it.
And look NOW he's STILL pursiing you while you made it CLEAR you wanted to work on your marriage...he's trying to BREAK UP your HOME...its perverse behavoir.
If you had a daughter and some guy was encouraging her to lie to YOU and run away from YOU, and he was calling your daughter even AFTER your daughter made it clear she doens't want to betray her family you would likley think the guy is a real ass.
Protect your home and your spouse like you would your children. This man should have sent you to counselling, or to talk to your husband, he NEVER should have gotten involved in something that wans't over to begin with.