I hope you don’t take this the wrong way, but if you love your girlfriend you’ve most likely accepted and love her child as well? You need to think about what’s best for the child and having his parent involved in his life is a part of that. That child deserves all the love they can receive and you have to replace the selfishness with selflessness. YOU may not want him around but that baby will resent you if you make their relationship with their parent any harder than it already is. Let your SO deal with the ex. As someone who had a horrible step father that controlled everything in my life and not my MOM I HATED him. Don’t let that be you. Be a friend (still have your boundaries) but the last thing a child wants is another person giving them rules.