Am i stupid or just in love soo deep????

ok i have been with this guy for 4 yrs.we have a six mth old son together .we were broke up aug06-mar07 as soon as we got back together i got preganant.he promise everything would be different this time .to make a long story short he cheated on me bad ,i caught him with a cell phone i never knew he had . hes acts like hes mad at me and leave for 2 and 3 days at a time and come back he has been doing this since feb.i always accept him back .i called one of the girls out of several he had been dealing with she said she had with him and she has been with him she told me this in apr its now jun she sent me a message telling me how could i be so stupid to let a man step out on me but thats ur problem not mine .i felt so stupid .he left again jun 1 today is now jun 15 .i asj him to come back home he told me no .i know i deserve better but my son is only six mths old.i just cant believe im going to be a single mom so early.what should i do.please real advice only