why did he dump me so quick

i am so mad and sad at the same time my boyfriend of a year and a half just dumped me 2 weeks ago he was supposed to come over on friday after work we had talked a few times that day on the phone and later when i had not heard from him i freaked i started texting him and calling him and nothing he just ignored me i should give you some details first about 3 or 4 weeks ago he moved into his friends house, there a married couple with 2 kids ,but they both abuse there prescriptions and drink and smoke weed, i was very worried about him moving there but i wasn't ready to let him move in my place yet we had tryed that last year and it didn't work out well, his friend has a sister who is divorced and living with her ex husband and i was worried that when she's there that something was going on well i was right when he quit talking to me and i spent a week trying to call him and text him he finally did talk it was his FRIEND that told me by text that they was dating and for me to leave them alone i'm so mad he told me he loved me right up to that day and we was going to get married i don't know how he just shut his feelings off and started dating somebody the next day and i do want to say he is bi polar and not on meds he quit taking them last year in Feb. before we met but he seemed so nice and sweet and the most caring and loving person i had ever met and I'm 45 and hes 35 there is and age difference but that was never and issue,he broke up with before back in july when he moved in with his sister but we kept talking and worked it out but this times different he changed his phone number 1 week after all this started so i have no way to contact him and hes 45 min. away from where i live,he also has 2 ex wives and 3 kids but he only see's the youngest child from his last marriage his first wife moved away and he never see;s his 2 oldest kids ,and just to give you more info he has not been able to get and keep his own place for more than 5 months since i've known him because he pays so much out in child support he just seems to feed of other people and wants them to feel sorry for him,but besides all that i just can't seem to get over him ,i'm so mad that he is seeing this other woman and so suddenly after being with me she must be stupid she knew we was together and she is a rebound ,and i also wonder if he might come back ,i;m not sure i would take him back but i would love to say what i need to he just cut off all contact and disappeared.