cheating husband

my husband cheated and got the girl pregnant. the baby is 3 months old now. he is very regretful and even does everything I ask him. he even exchanged his truck for a suv that I can drive to college and work. before he would drive me to work, he would never let me have the car the whole day. I know he is kind of bribing me into forgiving him and easing his guilt. but we've been married 3 years 8 months and were still not pregnant. so it hurts knowing that I am the problem, when it comes to the lack of growth in our family. it's my final year at school and we had agreed that I would get pregnant when I'm done with school. I never used contraceptives during our marriage.....and in all this time nothing happened.