Please understand that he put himself in this situation by putting his penis in you. If he really didn't want another kid, there were several options available to him, including abstinence, vasectomy, and several other forms of birth control. That he's shifting the blame to you, and making it appear to you that this is All Your Fault and that your decision is responsible for divorce and the breakup of your family, is monstrously selfish and wrong of him. Your husband is looking for a way out and has found a convenient one. Trust me, even if you had the abortion, six months later he'd find some other reason he had to leave.
If you want this child, and it sounds like you do, please do not have an abortion. You will regret it till the end of your life. Above all don't have an abortion to save a marriage to a guy who behaves like this. I'm a very big pro-choice advocate and frankly am aghast at the way young girls jump into motherhood these days, and I've had some scares where the first thing I did was turn to A in the yellow pages. (Which also shows my age.) But if a woman doesn't want an abortion, then unless she's floridly mentally ill or completely overwhelmed with other children and responsibilities, there's no way in hell I'd counsel abortion.
He will have to "deal with" another child whether he divorces you or not. Again, he was in full control of his own penis. Don't let him guilt you into thinking this is your fault. Please go ahead with what you love and feel in your heart is right with a clear conscience.
As for your original question: I didn't want divorce. My marriage was beyond dead, not to mention horrible thanks to my ex's mental illness and passive-aggressive horribleness, but it seemed to me that my kid would take the brunt of the divorce, and that I could tolerate being married-but-living-apart till she was grown. My ex divorced me in a miserable, chaotic, needlessly expensive way (and again, it was all my fault).
Result: Yes, I think my daughter's borne the brunt of it. However, you couldn't pay me to go back, and while she's paid, I think she's also gained a mother who's free to be herself and act with strength, which means there's a very different feeling in the house now. Let me underscore that it sucks for her in a great many ways, and that she hurts from it, even though she can't remember a time when we all lived together. But no, I could not go back, especially now that I can see more clearly how my ex treated me.
I still feel divorce is wrong and irresponsible. I go to synagogue and see family after family that does what I'd meant to do. However, I think not one of those people would tell me I should've stayed married -- given the problems, I think all of them would have advised divorce and felt there was something perverse in staying. Absolutely no one there suggested I try to work things out with him; all who knew me reached out to help. I know one woman there who deals with similar issues at home -- her husband's often profoundly depressed, and when not depressed, he flirts madly with other women. It's been hell on her, and I can see her determination in raising her three kids with him. But again, I suspect most people there think she and the kids would be better off without him.
A bigger problem for me is the question of remarriage. I really don't want to deal with another man, or take care of another man, and I'm happy on my own. However, I really feel dd lacks something here, and frankly as she gets older and more independent I think it will be very helpful to have another grownup here helping to raise her, keep tabs on her, keep her in bounds, help teach her and lead by example. I think she's going to be hard to handle when she hits teen, rebellious and smart -- and I fear that the lack of real attention she gets from her dad will lead her to seek out other male attention.
She spends quite a bit of time with her dad, but she's terribly quick on the uptake emotionally, and within a few years I think she'll begin to notice that his devotion to her is really all about him, all about having someone admire and love and validate him. And I can see her telling him about her achievements, and him undercutting her and jumping in to tell her about what he did, and isn't it wonderful. I don't think that strickenness of his about other people doing well is going to go away just because the other person happens to be his child. So I hope to have some kind of alternate father figure in there for her by the time she's old enough to get herself in trouble.
Anyway, hth. Answer is no, I don't regret it, but it does leave me with a lot of work to do, and some of the damage I can't do anything about. Don't let him make you believe you're the one choosing divorce.