I HAVE A CHILD FOR MY EX, MY HUSBAND THINKS THE CHILD IS HIS

My name is Joy, but my life has become joyless because of a stupid mistake I made.
I am married with 4 kids, I will be 35 in June, my husband is very loving and my marriage has been filled with Joy, happiness and proseperity since I got married in 2007 even though at the time I married him he was not the love of my life, I have grown to respect and love him.


My first love Mike, did not value my love or respect me, even though I could give my life for him, he disrespected me at every given opportunity but I loved him. I had to abort for him atleast twice, because he said  he was not ready for it, even though he has a good job. The last time I refused to abort he beat me up badly then forcefully took me to a doctor friend of his who carried out the abortion. He accused me of trying to ruin his life and drove me out of his house, I begged and begged but he refused to have anything to do with me. That was when I met my husband, he was patient with me, I told him everything and he insisted he wanted to marry me. I actualy married him because I wanted to hit back at Mike.
In 2010, Mike came back into my life, he kept pestering me and telling me he made a big mistake letting me go, he refused to accept that I am now married.
Then one day he called me and told me he was very sick and at home, I went to visit him, I dont know how it happened but we ended up making love. I regretted it immediately afterwards and cut all ties with him till date, because I knew he planned it all along.  I later discovered I was pregnant, but since I had  also been with my husband, I dismissed the nagging thought that the pregnancy was his.
I gave birth to my first son, my third child, my husband was over the moon, but each time I look at my son I see Mike, He is now 3 years old, very different from his 2 sisters and his younger brother. The guilt is killing me, there is also the fear that people will soon notice what I am seeing. I love my husband and kids and I dont want to lose them.
Please how best can I handle this situation, I dont want him to find out from others.