Why does my boyfriend help his ex-wife ?

okay, my boyfriend has been living with me for the past 4 years and when we first got back together he came to me and his ex-wife found out and tried to break us up. but it didn't work and she has a man the one who she left my b/f for 16 years ago and there still together but she has been having him do things for there grown kids and grandkids which i understand for the grand kids but everyweek his youngest daughter is wanting money from him she doesn't work she lives in low housing so her rent is not much and the ex-wife is always telling him what he needs to do for the grand kids so he does it and then she got her car repoed and then he helps her with money for down payment but he tried to lie to me and not tell me he helped her but i found out and he tried to deny it but i don't understand why he is doing this for her and she tells him that her "MAN" can't help her or won't help her but why does he do this she is the one who left him for this "MAN". and i don't know why he keeps helping her ?