Let me start off by saying that you have a lot of courage for going through those things and having to make such a decision. I also want to sincerely thank you for your question, as I am sure many people go through similar experiences but are afraid to seek advice.
Abortion is definitely not an easy thing to bring up, but I think that you should give yourself some time before approaching the subject; after all, it’s only been three months. Give yourself some time to think, and in terms of disclosing any information to your ex, always go at your own pace in terms of what you feel comfortable with. It is a delicate situation and should be handled as such.
I think that eventually your ex-boyfriend needs to know in order for both of you to maintain a healthy and open relationship. He could also help you deal with it. However, I definitely think you deserve to take your time in disclosing details as well.
You also have to think about his reaction; he may be very understanding, sympathetic etc. or he could be very confused, perhaps angry, etc. There is no telling how he will react, so you must also be ready to handle that as well. It is difficult for me to predict how he will react; only you know him best. Depending on the circumstances of the break-up –whether he expected you to remain single or not- he could react one way or another.
Also, at this time, you seem to be in the process of getting back with him and it may be too early to disclose all this information. Once your couple is stronger and more stable, you should consider initiating a discussion with your boyfriend at an appropriate time when you are both relaxed and have ample time for explanations.
If you are still dealing personally with the aftermath of the abortion, you should consider talking to a school counselor or psychologist about this- it is important you do know stay with emotional sequelae long after this happened.
Best of luck to you and please do not hesitate to write again if you need further help,
Catherine, for AlterHeros