You asked how it happened. Well the pill isn't 100%, but it's near as damn if taken properly and no sickness. So have you been unwell? I presume you didn't miss any? Did you take them at roughly the same time each day? How long have you been on it?
But that aside, you are where you are now...& you just have to decide where YOU want to be & given you can't go back in time... you have 3 options. If you don't think you could have the baby & have it adopted, then you're quickly down to 2 options.
Toss a coin!
Seriously, it'll give you your instant gut reaction!
Obviously you don't do whatever the coin 'says' , but it'll help you decide how you feel.
You have to assume you'll be raising the baby on your own, although it's not what you wanted if you had another child, you know you can do it and in much better circumstances this time. On the other hand, you don't have to if you don't want to!
What I would strongly advise though, is to think very carefully about what you want, before you tell him, because his immediate reaction (either way) may not be how he feels in time.
I'm a bit confused as to why you broke up, but I wouldn't want the baby or the termination to be the reason to get back together or stay separated.
Personally, at 33, I'd keep the baby, pick my moment to tell him & enjoy doing it a second time around in better circumstances.
But you're the only one who can decide 💐