My boyfriend cheated twice with a woman he still works with. am i stupid to think he wont do it again with her?

Well he had an affair with a woman from his work for two months before i caught him out. i stayed with him but he refused to leave his job. in the year since iv been trying to get over it and also we decided to have a baby his idea but ofcause i wanted this too. but at times its been too hard to handle what he did as i feel he is not making enough effort and ive left him a few times but gone back because he says hel try harder to help me forgive him. the last time i left within a day he met up with this woman slept with her while all the time begging for me to come back which i needed to see. ofcause i did and then found out from the woman hed slept with her again, how can he do that when thats all iv been worried about for the past year! i kicked him out for 3 weeks but ended up giving him yet another chance for the baby i guess and i do love him. he said he will leave his job but its been 3 months now and no effort to leave.