About 4 months ago XP decided he didn't want to continue our relationship, packed his bags and left the next day. The relationship had been a bit flat at that time as we had his brother living with us (who was a nightmare), DS had been ill (catching everything going at nursery) and my mum was admitted to hospital with pneumonia. I thought we could have worked on it, he disagreed stating once he'd left that he had no feelings for me.
At that time, he knew I only worked part-time and only earned minimum wage- with no savings, he wanted us out of the house and asked 4 DAYS after he'd gone when we would be moving. Eventually after having a house fall through that I'd got my heart set on (my parents agreed to loan me the deposit) he agreed it would make sense for me and DS to stay in the house - I know that his reasons were not working enough hours that month and he couldn't afford to pay the rent as shortly afterwards he stopped paying rent and cancelled all bills, obviously leaving me up shit creek - until my tax credits were processed.
I found out 6 weeks ago that he'd uploaded a profile on an internet dating site a month before he told me it was over - using a picture of him and our son together as his profile picture. I politely asked him to take it down - he lied that he'd ever had a dating profile, and I believe he constantly lies to me about everything.
Since then, and despite massive efforts by me to keep things amicable, including unrestricted visits to his son (as I wanted to keep things as normal as possible for DS) and him coming to my house to see him as he moved in with a friend miles away and bending over backwards to allow him the time that fits in with his work schedule, he continues to treat me as the enemy, either not paying any maintenance to me for his son, criticising my parenting, telling me he'll be over on x, y, z day to see DS and then cancelling all of the days and leaving me to pick up the pieces.
Last month he stated that he had had a massive fine and would really struggle to pay maintenance, I agreed telling him that it was a 'one off' and I couldn't cover him for any longer than one month.
Tonight he dropped DS off and then told me he couldnt afford maintenance again this month and do I really need all the money, in the next breath he said I'm going to a theme park friday and down to London on Saturday and his new gf will be there (he has him Saturday and Sunday) - despite me asking him to wait for a few months to see if she was right for him as I didn't want him being introduced to a string of women.
I am particularly annoyed, as when we were together all money we had was spent on him and him doing what he wanted (as he was main breadwinner) and I couldn't get through to him that DS also needed money spent on him for clothes/toys etc.
How do I get through this and put my foot down with XP so that he doesn't keep taking the piss? I'm not great at confrontation but cannot spend the rest of DS's childhood being spoken to like I'm an imbecile and I don't see why DS should have to keep going without things because his dad wants to spend the money that should be going on DS's upkeep on himself and his new GF.
Any advice would be gratefully received and apologies for the long post.