You need to be honest with yourself
You say you want everyone to be happy, actually you only want you and your boyfriend to be happy
You say your son has seen lots of your failed relationships, actually you want to continue with someone who has cheated on you twice already so are quite happy for your son to see yet another failed relationship
You son has got upset about the thought of having to live with this man, but actually you don’t care, you see this as him ‘ dictating’ to you when in fact he’s telling you how he feels
Your 15 year old son has more common sense and ability to see what’s going to happen than you. You are not a good role model, consistently putting your needs before those of your children and all you are showing them is how not to have a relationship, not how to have a good loving relationship with someone
HEs cheated twice he’s not a good example of how to behave either, yet you want him to be involved in your kids life!
He will cheat again, you will have a further failed relationship ( so might as well stop it now), your kids won’t thank you for this, you will be damaging your relationship with your kids, prepared to put a cheating man before them
Stop the relationship now, and build the relationship with your children