No one should be forced into a termination against their will. You clearly want to continue the pregnancy and that is your choice. If he chooses to leave then that is his choice but he will be the one missing out. I can't understand him asking you to have another termination knowing the impact the first one has had on your mental health.
He is using emotional blackmail in this instance and I wonder if he uses it elsewhere in your relationship. Think carefully about whether you want to be with a person who will do that.
You are afraid of him staying and resenting you but if you choose to terminate when that is not what you want you will likely resent him so it is a lose/lose situation.
Even if you start as a couple there is no guarantee that both parents will be around for their child as anything can happen. There is nothing wrong with being a single parent.
Your OH needs to realise that no matter what contraception is used if you have sex people can get pregnant and pregnancy leads to children. If he is so against having children right now he shouldn't be having sex as it is the only sure-fire contraceptive.
He used the same excuse last year and I am guessing he doesn't know when if he will ever be "ready". No one is ever really ready, as I understand it parenthood is one long learning curve.
If you choose to keep the pregnancy he may change his mind, it happens more often than you think, either way you will be fine. I personally believe men should have a degree of input with the choice regarding termination but the ultimate decision is the woman's alone and don't let anyone convince you otherwise.