In response to the post, I speak from experience. An affair in a relationship is never forgotten, though frequently it's forgiven. It does not mean long term happiness can not be achieved - unless of course, in addition, other factors impinge - like generally acting like a twat / bitch. In these cases the affair is generally the straw on camel whose back would have broken in any event.
An affair does change things; one is always henceforth keeping a watching eye. And it does take time for emotions to subside to manageable levels - and 2 years (2011 to now) is not a long time. Attitudes towards sex can take longer to reach normality but will soon follow on the heals of acceptance of things past and REAL forgiveness.
Forgiveness is the key. If you can truly forgive (that does not mean forget) and your man stays being "perfect" then you will have a long and happy marriage and your cute, beautiful gorgeous DS will have both a mummy and a daddy and will grow into a stable, confident young man - job done!!
The possible alternative is that your DS may (only may) grow up having some issues like a lack of self confidence. Just look at the evidence - kids who grow up in a 2 parent family do better at school, are less likely to have emotional problems etc. - and remember; exceptions prove the rule.
In addition, can you envisage this man; who after attempting suicide, who is so remorseful, who is trying so hard; being the sort of guy who will calmly accept that, "it's over", and regularly take his 50% of allotted DS time and conscientiously be a great dad to DS over the coming years?
Or do you think the pain of seeing you move on in life (eventually with another man) and the constant reminder of his mistake and failings and what could / should have been, will be far greater than the pain of abandoning his son? The latter is far more probable than the former - even if it starts differently it will soon become that way.
And how can you say that you will find a better existence elsewhere. You may swap one, "now perfect", man for a less perfect one; albeit without the pain of a past transgression. But is that better or just different - and what about the future of DS?
In the sphere of human relations, forgiveness is a most powerful tool; second only to love. If you can truly forgive then it will be OK. The length of time it takes to return to normality is inversely proportional to his continued efforts and your capacity to forgive. As normality returns, more positive attitudes towards sex so will also return.
Put in the balance on one side, these things:
your hurt emotions and pain, your wish to put it behind you, start again, find a new relationship with normal sexual emotions, the probability that if you do leave then it'll work out better for both you and DS,
and on the other:
your capacity to forgive plus the probability that if you do stay then it'll work out better for both you and DS
If you do decide to break then nobody will blame you but if you do decide to give it a bit more time, let him know his efforts are recognised and appreciated but also tell him that as a couple you're still not over the hill yet and maybe discuss with him your attitude to sex, maybe even together with a professional councillor.