Is Being with Him a Good Idea?

Aunty Amara, thanks for all the intelligent advice you give on your page. Aunty, I am drowning in confusion and I have to speak out. I dated this guy when I was in the university and he was my first love. We had a no sex relationship because I was a virgin. Aunty I love him to the moon and back.
There was this girl he once dated in the past. She doesn't want to let go. She kept coming around while we were together and he openly kept telling her off. She had other relationships but simply refused to let go of him. She knew how much he loved me and that made her to keep coming around to get me to react but I always kept my cool.
One of such days, he foolishly slept with her probably because he was sex starved by me and got her pregnant. This was what she actually wanted. Aunty that was where the gap between us started developing. He was running away from me because he was ashamed to face me. She had a baby boy and he is really taking care of them. He clearly told her and her parents that he wasn't ready for marriage but he was going to take care of them.
Aunty he is miserable now because he doesn't love her. He came back to me begging me to please forgive him. He said he is not happy being with her and he has seen he can't be happy without me. He was crying while saying all these. She went around saying he was her husband, she hated me so much because she saw me as a strong competition. Circumstances has tied him to her but his heart is with me. Aunty honestly I love him so much and have forgiven him.
But because he has a son now and that made the lady so present in his life, I don't know if being with him is a good idea. She is so desperate, she may even hurt me. I tried to move on but I still can't forget him. I need your advice please.

He may have been sex starved but that's not a valid excuse to undress himself and insert his penis into the vagina of an ex. That was a premeditated act and a decision he took to have sex with her. 
Good that he has realised his shortcomings,encourage him not to get married to a lady because of the presence of a child in their lives if he's not convinced that she's the one for him or he's not happy with her as his wife. This is because marriage is deeper than bearing children and you cannot make a lifetime decision because of a baby who can be taken good care of even if he decides to live with his mother. 
He can start all over again that is if he's willing to be a man and be faithful in his relationship. He can be trusted if his tears is from his heart and not from his eyes. You may reconsider him if he's not going to be sleeping around all in the name of being sex starved or because his wife isn't within reach for sex. 
On your own part, you must understand that the dynamics of your relationship and possibly marriage with him may not be the same because of the presence of his son. You have to make provision and accommodation in your heart to accept and appreciate his son just as you would appreciate him. You must learn to tolerate some of the disturbances and tantrums that the other woman may throw at him to get him and will be ready emotionally and psychologically and spiritually to stand with your husband in all circumstances and challenges that may confront him in the course of your journey with him. 
Well it all depends on what you and your partner can work out in times like this, whether he's genuinely in love with you and whether he's willing to stand by you and be faithful to you when he hopefully gets married to you. 
It's also depends on your state of mind and how prepared you are emotionally and spiritually to play the role of a wife, companion, friend and mother to him and his son in addition to your own children. 
If you have forgiven him and you are willing to give your relationship another opportunity to grow, maybe things will be much beautiful than it was in the past. 
If he hasn't performed anything on her head and he has decided to get married to another lady, I don't think that anyone else will hurt the lady all because he chose not to marry her. 
In all,seek the face of God and remember that nobody or nothing can hinder God from fulfilling his promises and purpose for his an individual irrespective of their shortcomings or the circumstances surrounding them. 
It's time to look beyond all that has happened and ask God to lead you to the man he has prepared for your destiny. 
God's convictions will dispel every form of fear or worries in your heart and help you make a better decision on what's best for you in your marriage.