I'm here
I cannot really say what i think you should do as it all depends on how reliable your ex is, what he's like and how your little boy is but i will tell you my story.
I split up with dd's father when she was 9months old, he left then came back when she was 2, left again when she was 3. When she was 5 I had to contact him about something and he said he would like to se her again but I said no cos i just couldnt trust him not to abandon her again. In the time he was gone he made absolutely no contact, no birthday cards or aything.
Then a few months ago he turned up on my doorstep, determined to see her again. She is now 6 and a half. He had now married his girlfriend (who is very nice which helps) and had a baby girl. My immediate reaction was to say no way again but I spent a couple hours talking to him and his dw. He was very determined to see dd and seemed to have grown up, a bit! He did also mention he would consider going to court for access.
I agonised over what to do but decided I would allow him to see her. I am terrified he will again get bored and abandon her when now she is old enough to really feel the rejection and heart break. BUT he is her father and if she can grow up seeing him on a regular basis, regardless how i feel about him, this has got to be better for her than growing up never knowing him and wondering why not. And I just know if she got in contact with him as a teenager/young adult he would blame me and say i refused him access, whether she believed it or not it would still be very painful for her i think. So i decided the risk of him hurting her by leaving was worth taking (now I feel the chance of that is not too high) compared to the damage it could do to her growing up wondering why he wasnt around. If I felt there was a higher risk of him buggering off again i think i would have said no, well i know i would! But I am doing everything i can to make sure it is done on my terms in the easiest, gentlest way possible. Also I feel if i say yes then I can do it my way and impose my terms on it, if i said no and he took me to court it would be imposed on us by someone who knows nothing of my daughter and what is right for her.
It is possibly the hardest decision i have ever had to make though, to let this man who has abandoned my baby girl twice already just waltz in and take her away for the weekend And it has really affected her, she has become very clingy and emotional and cries often when i leave her. But he is her father and I think I owe it to her to allow her the opportunity to have a good relationship with him.
Sorry to have waffled on so much, its has all happened very recently and i'm still in turmoil about it all!