My take:
I am a pro-choice person by default. I think all life should be allowed to exist and all children are wonderful creatures. I love my son, and wonder what the world would be like without him.
However, I am not sure who's choice this would be if it were not the woman's (it certianly is not our governments).
However, ethically speaking, by not allowing him a decision in this matter is not treating him like an autonomous agent and is thus unethical.
Every human, being human, demands the duty of being treated like an autonomous agent whenever possible. By not allowing him to have any say (although the ultimate decision is yours) you are depriving him of being treated like a cognitive agent.
In effect you have made a choice that impacts his life (whether he knows it or not) for him without his consent (let alone informed consent) and the ramifications of this decision could have great impact on his life.
If this decision you are making for two parties were made universal (in other words - if everyone in your decision did this) what impacts would this have on humanity.
Let me show you a scenario to illuminate my point.
You have the abortion and complications arise - you get ill, and have to disclose why you were ill. If this takes place, and he says that he would have taken this baby even if you did not want it (full custody) - you have impacted his life without his conscent. You cannot unring that bell once rung.
To reverse the situation I do not think you would want to have a childs life that you were paritally responsible for being terminated on anothers sole decision. I think if you decide to not tell him, you have not only failed the universibility test, but also the reversibility test.
Lastly, abortion in your case can seem like wishing to take actions and then not wanting to deal with the consequences of those actions. Assulting a person, and not wanting to go to jail. Eating whatever you want and not wanting to get fat. The want to shirk responsibility is a natural one - the reality however conspires against you.
I am not sure as though your intentions have any purity beyond 'this is inconvienient for me'. Love of the sperm donor has nothing to do with love of the child. Inconvienience and bad timing has nothing to do with the facts you have a growing child within you. If you see this decision as binary - have child and keep child - or abort - there is atleast one more option. Adoption.
What is needed for further analysis, personal and external, is your intentions. If your intent is to rid yourself of a being (or soon to be being) because of inconvienence then this needs to be factored in. If your intent is otherwise - then this needs to be factored in. If you do not know your intent but are making life altering decisions based on your lack of analysis - you may have created a situation where three beings (Sperm donor, yourself, and baby) are changed forever without real analysis. I think this has to be unethical.
One last thing. This has nothing to do with judgement, evil, good, or any of that **** the fundi's may lump on you. You have a decision to make - you need to make the right one and no amount of external help or pressure will change that fact.
God Speed.
TTF
p.s. I will adopt that child if it will change your mind. I am very serious. Good luck (if you believe in that sort of thing).