You'll need to go to a clinic or other abortion provider.
There are NO safe at home abortion methods. The abortion may not be complete, which could lead to severe infections, loss of fertility, or even YOUR death. It could also lead to you delivering a severely handicapped baby.
Like it or not, your former boyfriend WOULD be held responsible for child support if you decide to deliver. He's the father and it would be legally enforceable.
Placing the baby up for adoption is also an option.
At 3 months gestation you are looking at a surgical abortion - aspiration.
Contact planned parenthood. They can provide additional information.