please don't have sex with him. He is just taking advantage of the situation. If he has sex with you, he would be cheating on your mother. If your mom ever finds out, she would be so badly hurt.
And you would regret this later in your life.
And trust me, if your mom ever knows that you are hiding these cuts from her, she might be even more sad.
Please find someone, to whom you could tell this entire situation. For example, your guidance counselor. Or maybe a friend's mom or a teacher.
but please don't have sex with him. Don't do this to yourself.
I am here, if you need me. I could give you my email id of you want. Or you can reach me on Kik.