It sounds as if math is his main problem. My sister is in college (after taking 10 years off) and she has a math LD. Maybe discalculia? Not sure. Anyway, she takes the very basic of math classes in college, but is normal in every other subject. The ironic thing is that I majored in Math in college!! LOL!! Anyway, back to your son, I am learning that there is LOTS of help for college students just like any other school. Check out some college websites to get an idea and see the special resources they have for students with LDs. It's pretty amazing.
And like the other post, does he even want to go to college? If he does then I'm sure he will get whatever help he needs. Be sure to let him know that he can get help in college as well so he doesn't fear that it is a mountain he cannot climb. And to me, the great thing about college is that you can take your time. Just take a few classes at a time. It's not like HS where he has to be enrolled full time.
I always question whether my dd will even want to go to college since she too has an LD. I figure why would she want to sign up for more of the same of something that is difficult? But you never know. If she has an area where she excels then she will have a niche and do just fine and so will your son.
As to homeschooling, I know nothing about it. If it's just math where he struggles, then what about a math tutor or an educational therapist of some kind to work on his math abilities. My dd struggles to learn her addition facts (she just finished 2nd grade) and I'm realizing now that she is not visualizing. So, yesterday when I asked her what 2+1 was she did not know. So, I asked her to picture 2 ice cubes, so she closed her eyes and saw 2 ice cubes, then I said, keep your eyes closed, now here comes another one. How many do you see now? And she said "3"!!! So, it's not just "math" that is hard, but the underlying skills involved in learning it and understanding it.
Can you homeschool part time? Can he take regular English, history, etc.... and then homeschool for math or whatever subject he struggles?
Kathryn