What should you do if you're in love with your ex-boyfriend and he still loves you but you're both with other people and have kids?

Grow up and be responsible. Take care of your kids, have a loving relationship with your husband and get over it.If you go to your boyfriend, something will happen and you'll be wanting to move on again. It sounds like you have some maturity issues. Maybe you should see a marriage counselor.  

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decide whether or not you two want to be in the relationships your presently in and if you don't want to be in those relationship separate from those relationships and get together no one can exactly tell you what you should do just follow your heart it will know what to do!!!  

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When you had children, you made a committment to raise them. Stop being selfish and only thinking about your love life. Think about your children and keep your family together. Children from broken homes have a higher chance of dropping out of school, being involved in drugs, crime and gangs. Do the right thing for them and stop all contact with this ex-boyfriend.
Move to another state if you need to, but keep the ex out of sight, out of mind! The feelings will taper off. Work on your relationship with your current man (get married if you are shacking up). Start thinking about your children's future.